IB A15.1 PV Diagrams and Work

Get the Formative Assessment: FA15.1.docx

How to solve the Formative Assessment:

This is a Pressure v Volume graph for 0.280 mols of an ideal gas.

The system starts at a pressure of 175. Pa and a volume of 1.60 m³ and goes through these four processes:

Isobaric (constant pressure) compression to 0.400 m³
Isochoric (constant volume) cooling to 50.0 Pa
Isobaric expansion to 1.60 m³
Isochoric heating to 175 Pa

Draw all four processes. Use arrows for the processes, and label each process 1, 2, 3 or 4

1. Calculate the highest and lowest temperature (in K) Label these temperatures at the corners on the graph above.
(8.60 K and 120. K)

2. Calculate the work done by each process, and the net work done by the gas in the entire cycle.

(1: -210 J, 2: 0, 3: + 60. J, 4: 0 Net work = -150 J)

Problems like this:

Single processes:

Complete cycles:

PV Cycles Example 1

PV Cycles Example 2

PV Cycles Example 3

PV Cycles Example 4

3. At what temperature in Celsius does 14.0 grams of Helium have a total internal energy of 9450 J?
(He = 4.003 g/mol)

(-56.4 ^oC)

Problems like this:

Internal Energy WB#1

Internal Energy WB#2

Internal Energy WB#3

4A&B.

4A. 32 J of heat flow into a gas, and its internal energy drops by 17 J, how much work did the gas do? Does the temperature rise or fall? (Answer both questions)

(+49 J of work, temp falls)

4B. Fred does 35 J of work compressing a gas in a cylinder, and the internal energy rises by 13 J, what is the amount of heat flow into the gas? Does heat flow into or out of the gas? (Answer both questions)
(-22 J, heat flowed out)

Problems like this: (These proved to be vexing when they were on the test - I would do all of them on the 15 worksheet I gave you)

Q = U + W Example 1

Q = U + W Example 2

Q = U + W Example 3

5. What is the change in entropy of 1.20 kg of water boiling into vapor at 100.0 oC? (L = 22.6x105 J/kg)

(+7270 J/K)