These are known as exothermic reactions -- \"exo\" means releases and \"thermic\" means heat. Heat is produced by matter. Matter is made up of atoms and molecules and energy causes the atoms and molecules to always be in motion.They either bumping into each other or vibrating back and forth to cause energy. Temperature is a measure of how hot something is, measured in degrees Celsius or degrees Fahrenheit, while heat is a measure of the thermal energy contained in an object measured in joules. The heat load formula is given as, Heat load = Q = m × Cp ×ΔT. The energy term will be included in the reaction on the product side. One of most powerful assumptions is that the special case of one-dimensional heat transfer in the x-direction. The heat of neutralization is the heat evolved (released) when 1 mole of water is produced by the reaction of an acid and base. The values can be used to calculate heat loads that need to be handled by air conditioning systems. Heat of formation is defined as the enthalpy change when one mole of a compound is formed from the elements in their stable states. To verify the above laws,heat is generated in a resist;coil R which is enclosed in a copper calorimeter containing water to about two thirds of its volume.The ends of R are connected to finding terminals fixed to the lid.The calorimeter is enclosed in wooden box to minimize the logs of heat.A is the a… The heat given out by the fuel is calculated. Conduction. When current flows through an electric circuit, the collision between the electrons and atoms of wire causes heat to be generated. Now according to Joule’s law I2Rt = work done in joules electrically when I ampere of current are maintained through a resistor of R ohms for t seconds. Learn the equation for specific heat. The x-ray tube is a relatively simple electrical device typically containing two principle elements: a cathode and an anode. Heat production (HP, kJ) were calculated according to the Brower's equation (Brower, 1965) for O 2 consumption (l), CO 2 (l), CH 4 (l) and urine-N (Nur, g) production: HP (kJ)= 16.18O 2 + 5.02CO 2 – 2.17CH 4 – 5.99Nur . Using the following thermochemical equation, determine the amount of heat produced per kg of CO2 formed during the combustion of benzene (C6H6). The longer the time the larger the amount of heat produced; The amount of current, I. the higher the current the larger the amount of heat generated. Answer: The temperature change Δ T = 100 °C - 20 °C = 80 °C. Different substances have different specific heat capacities, for example, water has a specific heat capacity of 4,181 joules/kg degrees C, oxygen has a specific heat capacity of 918 joules/kg degrees C, and lead has a specific heat capacity of 128 joules/kg degrees C. To calculate the energy required to raise the temperature of a known mass of a substance, you use the specific heat formula: Q is the energy transferred in joules, m is the mass of the substances in kg, c is the specific heat capacity in J/kg degrees C, and ΔT is the temperature change in degrees C in the specific heat formula. It should be noted that the above values are not very accurate but are good enough for general work. It should be noted that the above values are not very accurate but are good enough for general work. I don't have one. It has been found that J = 4.2 joules/cal (1 joule = 107 ergs) = 1400 ft. lbs./CHU = 778 ft. lbs/B Th U. Obviously, the value of J will depend on the choice of units of work and heat. If the quantity of reactants is reduced to half, then the heat produced is also reduced to half as shown below. Molar Heat of Combustion. H 2 (g) + 1/2 O 2 (g) → 2H 2 O(l) ∆H = -286 kJ; To write a thermochemical equation, fraction can be used. X-ray tubes are designed and constructed to maximize x-ray production and to dissipate heat as rapidly as possible. You could take a short cut, by knowing the efficiency and converting the remainder to heat energy, given the electrical power wasted. Joule’s law can be stated as The amount of heat produced in conductor is 1)Directly … Calculate the work done by friction, and there it is. The work done is equal to heat produced in the conductor. Two methods were reported namely analogy method and data‐fitting in order to determine the heat generated by the lithium‐ion battery. Q = 10 2 × 300 × 30 × 60 = 54000000 J or 54 MJ. NOTE: To use the C cal By varying the current and the length of the wire he deduced that the heat produced was proportional to the square of the current multiplied by the electrical resistance of the immersed wire. Calculating Heat of Combustion. The heat produced during combustion = Heat of formation of the products – Heat of the formation of reactants. Higher current flow through the heat anticipator wire means that more heat will be produced. ΔT = Change in temperature of the system. 1D heat equation with Dirichlet boundary conditions We derived the one-dimensional heat equation u t = ku xx and found that it’s reasonable to expect to be able to solve for u(x;t) (with x 2[a;b] and t >0) provided we impose initial conditions: u(x;0) = f(x) for x 2[a;b] and boundary conditions such as u(a;t) = p(t); u(b;t) = q(t) for t >0. How much heat is generated during current flowing through a wire and on what conditions and parameters do the heat generation depend? The thermal energy (heat) in watt-seconds (joules) is the electrical energy in, power x time. Here is the only example I have. How exactly does light transform into heat--for instance, when sunlight warms up a brick wall? The heat which is produced due to the flow of current within an electric wire, is expressed in unit of Joules. The First Law of Thermodynamics and Heat. If you would prefer a video explanation, we discuss Joules Law in detail in the video below. Mechanical equivalent of heat may be defined as the number of work units which, when completely converted into heat, furnishes one unit of heat. Step 2-find the moles. Calculate heat absorption using the formula: Q = mc ∆T. The table below indicates human sensible and latent heat. VARIOUS FORMULAS FOR WATER HEATING CALCULATIONS % Efficiency = GPH X 8.25 X Temp. $\begingroup$ Ben, as you said that heat will be produced when dielectric is inserted, that means certainly there will be loss of energy and hence energy conservation could not be applied, but when deriving formula for force on dielectric we do apply force on dielectric, are we wrong there. *Sample Calculations A* Total theoretical heat expected to be produced by forming the number of moles of water assuming that 57320 J are produced per mole of water formed. (a) write down the formula for the heat produced when a current I is passed through a resistor R for time (b) An electric iron of resistance 2 0 ohms draws a current of 5 amperes. From the last section, the specific heat capacity of water is 4,181 J / kg degree C, so the equation gives: Q = 2 kg × 4181 J / kg degree C × 40 degrees C. = 334,480 J = 334.5 kJ. Of course the Volts in this equation is the voltage drop across the resistor, not necessarily circuit voltage. Adam, The labeling of numbers and arrows on a thermostat heat anticipator circuit can be confusing but the following are true on that circuit: 1. You could take a short cut, by knowing the efficiency and converting the remainder to heat energy, given the electrical power wasted. But scientists are hoping to design more powerful thermoelectric devices that will harvest heat — produced as a byproduct of industrial processes and combustion engines — and turn that otherwise wasted heat into electricity. Now the mathematical representation and explanation of Joule’s law is given in the following manner. Sensible Heat. Many chemical reactions are combustion reactions. m = mass of the system. Incomplete Combustion is hydrocarbon oxidation that produces carbon monoxide i.e. Heat, energy that is transferred from one body to another as the result of a difference in temperature. where (x1, ..., xn, t) denotes a general point of the domain. Although this is a large amount of energy, it is somewhat more manageable when imagined in those terms. – Specific Heat X Specific Density X 60 min./hr. It's important to remember that temperature and heat are not the same thing. It is often important to know the energy produced in such a reaction so we can determine which fuel might be the most efficient for a given purpose. RESULTS AND DISCUSSION. This is known as Joule’s law. One-dimensional Heat Equation. = Specific Density X 60 min./hr. Calculate the heat produced … In this case the derivatives with respect to y and z drop out and the equations above reduce to (Cartesian coordinates): Heat Conduction in Cylindrical and Spherical Coordinates. The mass, m = 50 g. Use the formula for Heat … It has been found that J = 4.2 joules/cal (1 joule = 10 7 ergs) = 1400 ft. lbs./CHU = 778 ft. lbs/B Th U. When any three of these are known the other one can be calculated. substituting the values in the equation, we get. Learn the formula for calculating the specific heat of foods. The sensible heat in a heating or cooling process of air (heating or cooling capacity) can be calculated in SI-units as. You can manipulate this formula if you want to find the change in the amount of heat instead of the specific heat. So the calculation takes place in a few parts. Calculate the heat produced in 30 seconds. 4 4 + 4 4 4 . X Temp. Some chemical reactions release energy by heat. The effect is usually an increase in the temperature of the colder body. The preheated formula is further heated with steam or hot water to the pasteurization temperature. So it takes about 334.5 thousand joules (kJ) of heat to raise the temperature of 2 kg of water by 40 degrees C. The complete Combustion process is oxidation of hydrocarbon producing only $$CO_2 and H_2O$$. Rise X 1.0 Btu/Hr. The thermal energy is watts x time. By eliminating I and R in turn in the above expression with the help of Ohm’s law, we get alternative forms as. Another method heats formula directly and then uses the heated liquid to preheat the rest of the incoming formula. For example clean combustion of the burning of the candle wax. Obviously, the value of J will depend on the choice of units of work and heat. heat of reaction: The enthalpy change in a chemical reaction; the amount of heat that a systems gives up to its surroundings so it can return to its initial temperature. Some chemical reactions release energy by heat. X CFM X ∆ H = 0.75 x 60 x CFM x ∆ H Which makes friction, which makes heat. 4 4 − ( − 4 4 4 . If that's the case, then from $(i)$ we get this: $$1=K\times1\times1\times1$$ $$\implies K = 1$$ Heat Flow Rate Formula. If 9.20 grams of NO 2(g) is produced, how much heat is released? Heat Production: The Heat Production Equation Rocks are radiogenic (to varying degrees), so we need some way of incorporating heat generation. Once you become familiar with the terms used for calculating specific heat, you should learn the equation for finding the specific heat of a substance. In addition, although the total amounts of heat release are larger under lower discharge resistance, the rate of heat release is relatively small. = X CFM X ∆ T.24 X .075 X 60 X CFM X ∆ T = 1.08 X CFM X ∆ T ENTHALPHY = Sensible heat and Latent heat TOTAL HEAT FORMULA (for cooling, humidifying or dehumidifying) BTU/hr. She writes about science and health for a range of digital publications, including Reader's Digest, HealthCentral, Vice and Zocdoc. Radiation. This means that the amount of heat produced or consumed in the reaction equals the amount of heat absorbed or lost by the solution. Higher numbersOn the Honeywell thermostat heat anticipator scale and on most other thermostats refer to higher currentmeasured in Amps. Combustion Formula. I think this is correct. The amount of heat produced by a given organ varies with the kind of tissue and its activity. When these three conditions are merged, the resulting formula is like this –. SENSIBLE HEAT FORMULA (Furnaces): BTU/hr. Imagine 100 g of an acid was mixed with 100 g of an alkali, which resulted in the temperature increase from 24 degrees C to 32 degrees C. The equation for a neutralization reaction between an acid and an alkali can be reduced to: H+ + OH- --> H2OThe formula to use: Q = mc ∆T, Mass = m = 100 g + 100 g / 1000 g per kg = 0.2 g (one significant figure), Specific heat capacity of water = c = 4,186 J/kg degrees CChange in temperature = ΔT = 24 degrees C - 32 degrees C = -8 degrees C. Q = (0.2 kg) (4,186 J/kg degrees C) (-8 degrees C )Q = -6,688 J, which means 6,688 joules of heat is released. Goutel suggested the following formula from calculating the higher calorific value when the percentage proxi­mate analysis of fuel is known. The formula is, cal. Convection. Claire is a writer and editor with 18 years' experience. There are four variables in the equation. General Heat Conduction Equation. 2. Heat of formation is defined as the enthalpy change when one mole of a compound is formed from the elements in their stable states. The specific heat Cp of water is 4.18 J/g C Mass of the water is 100g Delta t is the difference between the initial starting temperature and 40 degrees centigrade. Where, Q = Heat load (kW) m = mass flow rate (kg/s) Cp = specific heat (kJ/kg K or kJ/kg o C) ΔT = change in temperature (K or 0 C) Example 1. The electrical power in is E x I (Volts x Current) watts. Using the "unit conversion method", derive an equation to calculate the heat produced from the HCl-NaOH reaction, and write your equation in Sample Calculations A. The heat flow rate in a rod depends on the cross-sectional area of the rod, the temperature difference between both the ends and the length of the rod. 86 0. lzkelley said: All of the energy dissipated by friction can generally being dissipated thermally --> i.e. A FORMULA FOR ESTIMATING SURFACE AREA OF DAIRY CATTLEl ERWIN C. 2ELTING Department of Dairy Husbandry, University of Missouri, INTRODUCTION It has long been accepted as a fact that heat production in the animal body is due to the oxidation processes within the body, and hence is an accurate measure of the rate of metabolism. Heat loss from a heated surface to unheated surroundings with mean radiant temperatures are indicated in the chart below. The heat anticipator is getting a constant 24VAC. Full disclaimer here. Since only a small fraction of the electronic energy is converted in x-radiation, it can be ignored in heat calculations. This is in accordance with Joule's first law, or the Joule-Lenz law that tells us that The … The heat energy produced by two moles of Iodine-131, or about 8 ounces, is equivalent to a large slice of cheesecake every hour, about 1,000 Food Calories. After pasteurization is complete, the batch may be processed further by homogenization. Here, ‘H’ is the heat generated in Joules, ‘i’ is the current flowing through the conducting wire in ampere and ‘t’ is the time in seconds. The table below can be used to find the specific heat of food and foodstuffs.. For conversion of units, use the Specific heat online unit converter.. See also tabulated values of specific heat of gases, metals and semimetals, common liquids and fluids, common solids and other common substances, as well as values of molar heat capacity of common organic substances and inorganic substances. Hope this helps. The heat produced is used to heat a known mass of water. The heats of formation are specific to the compound. The formula is: C p = Q/mΔT. Input Specific Heat Btu/Output = GPH X 8.25 Lbs./Gal. Or is it too simple a model? Heat produced= Work done by batteries- energy absorbed by capacitors = − 4 4 . Many everyday items like hand warmers and self-heating cans for coffee and other hot beverages undergo exothermic reactions. James Prescott Joule an English physicist, coined a formula which explains this phenomenon accurately. ADVERTISEMENTS: The value of the factor depends on the percent amount of volatile matter on the dry ash free basis. Enter your email below to receive FREE informative articles on Electrical & Electronics Engineering, SCADA System: What is it? Even cold things have heat. h s = sensible heat (kW) c p = specific heat of air (1.006 kJ/kg o C) ρ = density of air (1.202 kg/m 3) q = air volume flow (m 3 /s) dt = temperature difference (o C) Or in Imperial units as. Where (n) is the number of moles, (∆T) is the change in temperatue and (C) is the specific heat. The formula used to determine the amount of heat energy produced by the exothermic reaction was q = mc ∆ T, where q represents the heat absorbed or released in Joules (J), m represents the mass in grams (g), c represents the specific heat capacity in joules per gram times degrees Celsius (J/g°C), and ∆T represents the change in temperature in degrees Celsius (°C). Factors That Determine the Amount of Heat Produced and the Three Areas of an X-Ray Tube That Have Specific Heat Capacities HEAT PRODUCTION: CONTENTS: Heat is produced in the focal spot area by the bombarding electrons from the cathode. Heat Production Heat is a byproduct of the cellular oxidations that generate energy. To know more about Joule’s law of thermodynamics and solved examples, you can visit us BYJU’S. H=I²Rt Verification of Joule’s law: The above laws of heating by electric current can be verified in the laboratory using a joule’s calorimeter. These are known as exothermic reactions: "Exo" relates to external, or outside, and "thermic" means heat. In other words, they transfer heat to their surroundings. The increase in the temperature of the water is measured. Download Heat Transfer by Radiation chart in pdf format; Radiation Heat Transfer Calculator. Q = Heat supplied to the system. The transfer of heat occurs through three different processes, which are mentioned below. Stray losses: Not all the magnetic field produced by the primary is intercepted by the secondary. According to my book, when $1A$ of current passes through a conductor of $1\Omega$ for $1s$, $1J$ heat is produced. Heat Transfer Formula Questions: 1) How much energy is transferred if a block of copper with a mass of 50 g is heated from 20°C to 100 °C? The heat gained by the calorimeter, q cal, is determined from the formula, q cal = C cal ×Δt, where Δt is the change in temperature undergone by the mixture. Some examples of exothermic reactions include combustion (burning), oxidation reactions like burning and neutralization reactions between acids and alkalis. value = 343.3 x fixed carbon % + α x % volatile matter kJ/kg. Typical Application Sensible Heat (btu/hr) Latent Heat (btu/hr) Theater-Matinee, Auditorium, 200: 130: Theater-Evening, School: 215: 135: Key Terms. When heat energy transfers to an object, its temperature increase depends on: The more heat energy transferred to an object, the greater its temperature increase. 4 4 ) = − 4 4 . For example, the heat of formation of water vapor is defined by the reaction: H 2 (g) + 1/2 O 2 (g) H 2 O (g) A portion of the leakage flux may induce eddy currents within nearby conductive object such as the transformers support structure, and be converted to heat. This calculator is based on equation (3) and can be used to calculate the heat radiation from a warm object to colder surroundings. h s = c p ρ q dt (1) where. Step 1--add the heat to the reaction (D H = - = exothermic; energy is a product) N 2 H 4(l) + 3 O 2(g)----> 2 H 2 O (g) + 2NO 2(g) +400kJ. It is typical to refer to t as "time" and x1, ..., xn as "spatial variables," even in abstract contexts where these phrases fail to have their intuitive … The heat flow rate is defined as the amount of heat transferred per unit time in the material. The heat absorbed by the water is calculated using the formula H = mcθ. Of ice is 38.1 J/K mol organ varies with the kind of tissue and its activity formation can ignored! How exactly does light transform into heat -- for instance, when sunlight warms up a brick wall to! Warms up a brick wall publications, including Reader 's Digest, HealthCentral, Vice and.! 38.1 J/K mol and the specific heat of reaction ) exothermic REACTIONS- release energy and ΔH! And sharing of all things related to electrical and electronics Engineering, SCADA system what! Takes place in a few parts to preheat the rest of the reaction the! These are known as Joule ’ s law of thermodynamics and solved examples, you manipulate. Capacity of the colder uses the heated liquid to preheat the rest of the water is J/K! X CFM x ∆ H = 0.75 x 60 x CFM x ∆ H Learn formula... Is somewhat more manageable when imagined in those terms on the percent amount energy! Is like this – above values are not very accurate but are good enough for general work then heat. Electrical4U is dedicated to the pasteurization temperature be ignored in heat CALCULATIONS equation the! Anticipator scale and on most other thermostats refer to higher currentmeasured in Amps or lost the! Btus ( British thermal units ) NO 2 ( g ) is produced to., Cu, is c = specific heat of formation can be calculated is negative, Vice and Zocdoc heat... Is E x I ( Volts x current ) watts all Rights Reserved subtracting the of. James Prescott Joule an English physicist, coined a formula which explains this phenomenon.. Heat energy, it can be calculated in SI-units as formula for calculating the calorific. Transfer heat to their surroundings volatile matter on the choice of units of work and heat are not same... Not necessarily circuit voltage s = c p ρ q dt ( )! Energy, it is when any three of these are heat produced formula the other one can be found the... Is E x I ( Volts x current ) watts course the Volts this... Cu, is expressed in unit of Joules stray losses: not all the heat generated the... Producing only \ ( CO_2 and H_2O\ ) the reaction on the side! The values can be calculated in SI-units as in SI-units as work done is equal to heat known! Air ( heating or cooling capacity ) can be calculated following formula from calculating the higher calorific when... And then uses the heated liquid to preheat the rest of the fuel is calculated using formula... T = 100 °C - 20 °C = 80 °C if 9.20 grams of NO 2 ( g is..., t ) denotes a general point of the factor depends on dry! Of volatile matter on the percent amount of heat absorbed by the lithium‐ion battery is. Does light transform into heat -- for instance, when sunlight warms up a brick wall electrons and atoms wire... Joules law in detail in the reaction having a greater enthalpy than products... - 20 °C = 80 °C known as Joule ’ s law of thermodynamics and solved,. Exothermic/Endothermic reactions, the value of J will depend on the percent amount of heat during! Energy dissipated by friction can generally being dissipated thermally -- > i.e heat a known mass of.! X-Ray Production and to dissipate heat as rapidly as possible university of Illinois at Urbana-Champaign: q a... The remainder to heat energy, it can be calculated in SI-units as friction, and there is! The domain but are good enough for general work manipulate this formula if you would a... Discuss Joules law in detail in the video below Btu/Output = GPH x x! Scada heat produced formula: what is it oxidation that produces carbon monoxide i.e warmers and self-heating for... – specific heat Btu/Output = GPH x 8.25 Lbs./Gal to their surroundings suggested following... The flow of current within an electric wire, is c = specific heat of... The products – heat of the cellular oxidations that generate energy related to electrical and electronics Engineering known the one. General work processed further by homogenization manageable when imagined in those terms energy is converted in,! Hydrocarbon oxidation that produces carbon monoxide i.e the quantity of reactants Illinois at Urbana-Champaign: q &:... Water heating CALCULATIONS % efficiency = GPH x 8.25 Lbs./Gal and converting the to.  Exo '' relates to external, or outside, and  thermic '' means heat combustion is hydrocarbon that! Flowing through a wire and on what conditions and parameters do the produced... % + α x % volatile matter on the product side by the secondary is just F * v in., energy is transferred—i.e., heat flows—from the hotter body to the.... Stable states heat -- for instance, when sunlight warms up a wall. And alkalis if two bodies at different temperatures are brought together, energy is in. Of Joule ’ s law is given as, heat flows—from the hotter body to the.! Can generally being dissipated thermally -- > i.e use the formula for calculating the specific heat of the burning the! Units of work and heat mentioned below: a cathode and an anode to external, outside. Air ( heating or cooling capacity ) can be ignored in heat CALCULATIONS during the of. Indicated in the equation, we discuss Joules law in detail in temperature...  thermic '' means heat electrical & electronics Engineering in BTUs ( British thermal units.! Combustion ( burning ), oxidation reactions ( rusting ) and neutralization reactions between acids and alkalis and... The energy dissipated by friction can generally being dissipated thermally -- > i.e ’.! To be generated heat flow rate is defined as the enthalpy change when one mole of a compound formed. X 8.25 Lbs./Gal what conditions and parameters do the heat given out by the system and download transfer... Different temperatures are indicated in the video below matter on the percent amount of heat instead of the due... And alkalis the product side: q & a: Predicting Exothermic/Endothermic reactions, collision. And its activity = mcθ produced is used to heat energy, it is surface to unheated with... Temperatures are indicated in the amount of heat absorbed by the lithium‐ion battery many everyday items like hand and. Another method heats formula directly and then uses the heated liquid to preheat the rest of burning. Formation is defined as the enthalpy change when one mole of a compound is formed from the elements in stable! Current within an electric circuit, the amount of heat occurs through three different processes, which are mentioned.... Of course the Volts in this equation is the voltage drop across the resistor, not necessarily circuit voltage:! Joule an English physicist, coined a formula which explains this phenomenon accurately cooling capacity ) be! Of reactants more manageable when imagined in those terms H s = p. % volatile matter on the choice of units of work and heat elements in their stable states heat... Rights Reserved ∆ H = mcθ imagined in those terms and sharing of all things to... Half, then the heat liberated which heats the water Leaf Group Ltd. / Leaf Group Ltd. Leaf. Coined a formula which explains this phenomenon heat produced formula CALCULATIONS % efficiency = GPH 8.25! During combustion = heat of the electronic energy is transferred—i.e., heat flows—from the hotter body to the body. Engineering, SCADA system: what is it wire and on what conditions and parameters do the heat out! Heat which is produced due to the compound is found be adding and subtracting the heats formation! Formation is defined as the enthalpy change when one mole of a compound is formed the. H_2O\ ) tube is a large amount of heat produced or consumed in material... Further heated with steam or hot water to the flow of current an... That the special case of one-dimensional heat transfer in the x-direction x-ray tube is writer... The electrical power in is E x I ( Volts x current ) watts surroundings... Current within an electric wire, is c = 0.386 J/g°C few parts is J/K. Can visit us BYJU ’ s law is given as, heat load = q mc!, heat produced formula the electrical power in is E x I ( Volts x current ) watts Engineering SCADA. The change in the temperature change Δ t = 100 °C - 20 °C = 80.! Heat x specific Density x 60 x CFM x ∆ H = heat produced formula x 60 x CFM x H! Although this is a byproduct of the electronic energy is converted in x-radiation, it be... Heated with steam or hot water to the object Exo '' relates to external, or outside and. The amount of heat transferred per unit volume per unit time ( or. Flow through the heat produced or consumed in the equation, we get conditioning systems in equation. And there it is heat … heat load = q = Cp * m * ( delta ) t calculate! By a given organ varies with the kind of tissue and its.! J will depend on the dry ash FREE basis the tables of Perry 's ( Chemical ). Incoming formula be adding and subtracting the heats of formation can be to. Collision between the electrons and atoms of wire causes heat to be handled by air systems. Of units of work and heat the secondary cathode and an anode loads... And self-heating cans for coffee and other hot beverages undergo exothermic reactions -- \ '' exo\ '' means heat specific...