This reaction could be performed under either constant press

This reaction could be performed under either constant pressure or constant volume conditions. (See Text: Thermochemistry.) a) What symbol is used for heat/mole measured under constant pressure conditions? b) What symbol is used for heat/mole measured under constant volume conditions? c) Under what conditions did you measure the heat of reaction? d) Assuming the same amount of Mg reacted, which value should be larger -the heat measured under constant pressure conditions or the heat measured under constant volume conditions? Explain.

Solution

A: Q = E ; heat per mole measured at constant volume

B: Q = H; heat per mole measured at constant pressure

C: The standard conditions for a reaction to carry out :101.3kP( 1atm) pressure and 25 degree Celsius temperature.

D: H= E+PV

Qp= Qv+ PV

Qv= Qp-PV. (W= --V)

So heat measured at constant pressure is high than heat measured at constant volume.