Endothermic reaction meansΔq is positive.
Exothermic reaction meansΔq is negative.
Work done by system meansΔW is negative. (work is leaving the system)
Work done by surroundings means ΔW is positive.
Agas is heated inside of a balloon with frictionless expansion. The balloon expands from
5 L to 5.7 L. The pressure inside the balloon and surroundings is 2.1 atm. What is the
change in work of the system? Surroundings? What can be done to the gas to ensure a 0
change in internal energy?
ΔW = -PΔV = -2.1(5.7-5) = -1.47 J
Adding heat would make sure there is still the same internal energy.
Awaterfall was examined. Temperature of the water at the top was measured along with
the bottom. If the waterfall is 100 m high and all potential energy is converted into
thermal energy, what is the temperature difference between 150 g of water at the top of
the waterfall and 150 g of water at the bottom of the waterfall? C sf water = 4.18
ΔE =P0.15 kg (9.8) (-100) = -147 J
- ΔE PΔE T
ΔE =T147 J
ΔQ = 150 g (4.18) ΔT = 147
ΔT = 0.23 K
A61 g hot piece of metal at 120 C is in 100 g of water at 20 C. The metal cools and the
water heats up until they are both at a temperature of 26.39 C. What is the specific heat of
the metal if the water has a specific heat of 4.18?
- ΔQ of me