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what are heat capacities at constant volume and pressure?\xa0 |
| Answer» Ans.\xa0The heat capacity of anything tells us how much heat is required to raise a certain amount of it by one degree. For a gas we can define a molar heat capacity C - the heat required to increase the temperature of 1 mole of the gas by 1 K.Q\xa0=\xa0nC∆T\xa0The value of the heat capacity depends on whether the heat is added at constant volume, constant pressure, etc.CV, the heat capacity at constant volume, and CP, the heat capacity at constant pressure.Heat Capacity at Constant Volume CV:\xa0Q = nCVΔTFor an ideal gas, applying the First Law of Thermodynamics tells us that heat is also equal to:Q = ΔEint\xa0+ W, although W = 0 at constant volume.Heat Capacity at Constant Pressure:\xa0For an ideal gas at constant pressure, it takes more heat to achieve the same temperature change than it does at constant volume. At constant volume all the heat added goes into raising the temperature. At constant pressure some of the heat goes to doing work.Q = nCPΔTFor an ideal gas, applying the First Law of Thermodynamics tells us that heat is also equal to:Q = ΔEint\xa0+ WAt constant pressure W = PΔV = nRΔT | |