Heat Flow Constant Volume hold fixed heat flows

Heat Flow

Constant Volume hold fixed heat flows at base to change temperature ] Fixing the piston keeps the volume constant. ] If heat flows in then temperature remains the same.

Isochoric Process ] For a constant volume process there is no work. • • ] DV = 0 W=0 P The internal energy change is only due to heat. • DU = Q – W = Q V isotherms

Specific Heat at Constant Volume ] At constant volume the heat equals the change in internal energy. ] A molar specific heat at constant volume relates to the change in temperature. ] CV can be defined from the internal energy.

Constant Pressure ] Allow the piston to move to keep the pressure constant. • Same on both sides ] move to maintain pressure heat flows at base to change temperature Heat flows in and the piston can do work.

Isobaric Process ] For a constant pressure process the work is a simple product. • ] P W = P (V 2 – V 1 ) The heat can be related to the internal energy change and volume change. • Q = DU + W • Q = DU + PDV V isotherms

Specific Heat at Constant Pressure ] The internal energy was related to the temperature change. ] A molar specific heat at constant pressure relates to the change in temperature. ] For and ideal gas, CP can be defined from CV.

Specific Heat for Gases ] ] The ideal gas law predicts a Gas simple relationship between He the two forms of specific heat. Ne • CP = CV + R N 2 • R = 1. 99 cal/mol-K O 2 CO 2 The table shows how close H 2 O real gases are to ideal gas C 2 H 6 behavior. CV 2. 98 4. 96 5. 03 6. 80 6. 20 10. 30 CP (cal/mol-K) 4. 97 6. 95 7. 03 8. 83 8. 20 12. 35

No Heat ] ] completely insulate to block heat flow Completely insulate the system. Allow the piston to move. ] Heat can’t flow, but work can be done. ] Equivalent process occurs when change is quick so little heat flows.

Adiabatic Process ] For an adiabatic process there is no heat flow. • ] DU = Q – W = – W P There a relationship that can be derived for ideal gases. V isotherms