### Given q and w, will a gas's pressure increase or decrease?

Posted:

**Tue Jan 17, 2017 9:57 am**From 2007 Midterm:

Given that a a gas sample expands, doing 536 kJ of work, while 214 kJ of heat is added to the gas:

a) Calculate DeltaU

b) Will the pressure of the gas be higher or lower when these changes are completed?

I understand Part A:

a) DeltaU = q + w. q is +214 kJ since the heat is ADDED to the gas. w is -536 kJ because the gas is DOING the work and EXPANDING. So DeltaU = 214kJ - 536 kJ. Therefore, DeltaU = -322 kJ.

However, I do not understand Part B. I know that the internal energy change is negative. What is the relationship between DeltaU and Pressure? I can think of PV = nRT. The moles are constant and R is a constant. How can I say that P changes, and in which direction?

Thank you.

Given that a a gas sample expands, doing 536 kJ of work, while 214 kJ of heat is added to the gas:

a) Calculate DeltaU

b) Will the pressure of the gas be higher or lower when these changes are completed?

I understand Part A:

a) DeltaU = q + w. q is +214 kJ since the heat is ADDED to the gas. w is -536 kJ because the gas is DOING the work and EXPANDING. So DeltaU = 214kJ - 536 kJ. Therefore, DeltaU = -322 kJ.

However, I do not understand Part B. I know that the internal energy change is negative. What is the relationship between DeltaU and Pressure? I can think of PV = nRT. The moles are constant and R is a constant. How can I say that P changes, and in which direction?

Thank you.