jogging on the beach

- she is jogging on the beach and thus doing work on the beach
- she's sweating so she's giving off heat
- delta U = Q -W
- Q is negative because she's losing heat, "give off" is hint
- W is positive because she's doing W on the beach

A gas expands, doing 100 J of work. How much heat must be added to this system for its internal energy to increase by 200 J?

- Q= W + change in U
- 100 + 200
- Q = 300 J

One mole of an ideal monatomic gas is initially at a temperature of
274 K. **(a)** Find the final temperature of the gas if
3260 J of heat are added to it and it does 712 J of work.
**(b)** Suppose the amount of gas is doubled to two
moles. Does the final temperature found in part (a) increase,
decrease, or stay the same? Explain.

a. change in U = Q - W

replace change in U with 3/2 nR (Tf-Ti)

solve for Tf

b. When there are more molecules to share the energy, the average energy gained per molecule is smaller, resulting in a decrease in the final temperature found in part (a).

Suppose 118 moles of a monatomic ideal gas undergo an isothermal
expansion from to , as shown in **FIGURE 18-28**.
**(a)** What is the temperature at the beginning and at
the end of this process? **(b)** How much work is done by
the gas during this expansion?

a. solve for temperature with PV = nRT

b. W = nRT ln (Vf/Vi), solve for W in kJ

What is the efficiency of an engine that exhausts 840 J of heat in the process of doing 360 J of work?

- first calculate Qhot, W = Qhot - Qcold
- then efficiency = W/W + Qc

heat and no cold? better make it hot! Woah, woah there Qc

An engine receives 660 J of heat from a hot reservoir and gives off
420 J of heat to a cold reservoir. What are **(a)** the
work done and **(b)** the efficiency of this engine?

- first calculate W, W = Qhot - Qcold
- then efficiency = W/Qh

hot and cold? you gotta work. Yes QqqqqHueeee Bob.

A reversible refrigerator has a coefficient of performance equal to 9.50. What is its efficiency?

??

Determine the change in entropy that occurs when 4.3 kg of water freezes at 0 °C.

delta S = -mLf/T

change C to K

On a cold winter’s day heat leaks slowly out of a house at the rate of 20.0 kW. If the inside temperature is 22 °C, and the outside temperature is , find the rate of entropy increase

delta S equals (negative rate in W/T) inside plus (positive rate in W/T) outside

change C to K

An 88-kg parachutist descends through a vertical height of 380 m with constant speed. Find the increase in entropy produced by the parachutist, assuming the air temperature is 21 °C.

delta S = mgh/T

COP for aircon

By definition for an air conditioner, the COP is *Q*C/*W*