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A calorimeter constant (denoted C cal) is a constant that quantifies the heat capacity of a calorimeter. [ 1 ] [ 2 ] It may be calculated by applying a known amount of heat to the calorimeter and measuring the calorimeter's corresponding change in temperature .
A major use of the integrated equation is to estimate a new equilibrium constant at a new absolute temperature assuming a constant standard enthalpy change over the temperature range. To obtain the integrated equation, it is convenient to first rewrite the Van 't Hoff equation as [ 2 ]
A reaction calorimeter is a calorimeter in which a chemical reaction is initiated within a closed insulated container. Reaction heats are measured and the total heat is obtained by integrating heat flow versus time. This is the standard used in industry to measure heats since industrial processes are engineered to run at constant temperatures.
Constant-volume calorimetry is calorimetry performed at a constant volume. This involves the use of a constant-volume calorimeter. No work is performed in constant-volume calorimetry, so the heat measured equals the change in internal energy of the system. The heat capacity at constant volume is assumed to be independent of temperature.
The left-hand side is the specific heat capacity at constant volume of the material. For the heat capacity at constant pressure, it is useful to define the specific enthalpy of the system as the sum (,,) = (,,) +. An infinitesimal change in the specific enthalpy will then be
At constant pressure, heat supplied to the system contributes to both the work done and the change in internal energy, according to the first law of thermodynamics. The heat capacity is called C p {\displaystyle C_{p}} and defined as:
The difference relation allows one to obtain the heat capacity for solids at constant volume which is not readily measured in terms of quantities that are more easily measured. The ratio relation allows one to express the isentropic compressibility in terms of the heat capacity ratio.
The higher heating value takes into account the latent heat of vaporization of water in the combustion products, and is useful in calculating heating values for fuels where condensation of the reaction products is practical (e.g., in a gas-fired boiler used for space heat). In other words, HHV assumes all the water component is in liquid state ...