Practice Problems:
1. A mysterious substance (80 grams, originally in a solid state) has a latent heat of fusion (melting) of 350 000 Joules/kg
and melts at a temperature of 20 °C. Determine the amount of energy required to melt the substance if it temperature is at
its melting point.
(ans: 28000 Joules)
2. A substance has a latent heat of fusion of 700 kJoules/kg. 80 000 Joules is transferred to the substance and it completely
melts but does not change its temperature. What is the mass of the substance?
(ans: 0.114 kg)
3. 40000 Joules of heat energy are transferred to a substance (2400 J/kg°C, 300 grams). If the orginal temperature is 5°C,
calculate the final temperature.
(ans: 60.55°C)
4. A substance (mass is 200 grams) is originally in a solid state (2100 J/kg°C). As a liquid, its specific heat capacity is
4000 J/kg°C. The substance has a latent heat of melting of 400 kilojoules/kg and melts at 70 °C. Originally, prior to any
heat energy being added to the substance, its temperature is 38°C. After heat has been added, its final temperature is 82°C.
Determine
a) the energy required to heat the substance to its melting point
(ans: 13440 Joules)
b) the energy required to completely melt the substance
(ans: 80000 Joules)
c) the energy required to heat the substance to 82°C
(ans: 9600 Joules)
5. The half life for carbon-14 is 5730 years. A specimen contains 800 micrograms of carbon 14.
a) What amount of carbon-14 will be remaining after 10000 years?
(ans: 240 micrograms)
b) At what time will the amount remaining be 300 micrograms?
(ans: 8100 years)
6. The mass of contaminated soil from a nuclear weapons test site contains 5 milligrams of strontium-90 (half life of 29.1
years). Calculate the time needed for the quantity to decay to 0.1 milligrams
(ans: 164 years)