Chem 14B Practice Problems: First Law of Thermodynamics

How much work does a gas perform at a constant pressure of 8.4atm as it expands from a volume of 2.0L to 4.5L?ΔU = +175J

W = +2128J (1. When gas expands, W=+; when gas compresses, W=- 2. It's an isobaric process because pressure is constant; W = PΔV or W = nRΔT 3. Remember, work is in Joules, meaning we have to convert L*atm to J)

4.5 moles of an ideal gas is heated at a constant pressure from 30C to 150C. Calculate the work done by the gas.

W = +4490J (1. It's an isobaric process because pressure is constant; W = PΔV or W = nRΔT 2. We need to convert Celcius to Kelvin)

a) How much work is required to compress a monoatomic gas at a pressure of 2.5x10^5 Pa from an initial volume of 0.015m^3 to a final volume of 0.010m^3? b) What is the change in internal energy of the system if the system releases 350J in this process?

a) W = -1250J (1. When gas expands, W=+; when gas compresses, W=- 2. It's an isobaric process because pressure is constant; W = PΔV or W = nRΔT) b) ΔU = +900J (ΔU = Q - W; internal energy = heat absorbed/lost - work done/performed on)

Calculate the change in internal energy. The system absorbs 720J of heat energy and the surroundings perform 300J on the system.

ΔU = +1020J (ΔU = Q - W) (internal energy = heat absorbed/lost - work done/performed on)

Calculate the change in internal energy. 400J of work is done on the system, and the system loses 225J of heat energy.

ΔU = +175J (ΔU = Q - W) (internal energy = heat absorbed/lost - work done/performed on)

Calculate the change in internal energy. The system absorbs 300J of heat and performs 500J of work.

ΔU = -200J (ΔU = Q - W) (internal energy = heat absorbed/lost - work done/performed on)