Heat Conceptual Questions KEY
1. Units
a.
b.
c.
d.
e.
f.
g.
Joules
°C, °F, K
J/kg°C
J/kg
kg m2/s2
Heat
A Calorie is a kilocalorie. There are 1000 calories in a Calorie.
2. Heat, Temperature, and Thermal Energy
a. Energy that flows form hot to cold objects.
b. Average kinetic energy of the molecules
c. Total heat energy (kinetic energy) of ALL of the molecules in a substance.
d. Equal temperature
e. The tea has a higher temperature, but the Pacific Ocean has a higher internal energy.
f. No. It is an energy that flows from a hot object to a cold, but an object does not contain it.
g. Same temperature. The 3 L has more internal energy since there are more molecules. Neither contain heat.
h. Heat flows from the boiling water to the thermometer. The liquid in the thermometer is heated, which causes
it to expand and rise.
3. Temperature Scales
a. Kelvin, Celsius, and Fahrenheit
b. Fahrenheit. When you compare the range from the freezing point to boiling point of water, the widest range
is with Fahrenheit, indicating that each degree represents the smallest change.
c. 0K is absolute zero, and is a theoretical temperature. 0°C is the freezing point of water.
d. ~20°C, 293K, 68°F
e. 0°C, 100°C, 273K, 373K, 32°F, 212°F
4. Thermal Expansion
a. As an object is heated, its molecules move faster and gain more kinetic energy, which spaces them apart more.
b. It increases.
c. No.
d. °C-1
e. (m)*( °C-1)*(°C) = m
f. Expansion joints in a railroad or bridge, water expands.
5. Specific Heat
a. Energy required to raise the temperature of 1 g of a substance by 1 °C.
b. It requires a lot of heat energy to change its temperature.
c. No, it is dependent on each substance’s specific heat, which is unique to each substance.
d. Yes, energy must be conserved, so the heat lost by one object in the mixture is gained by the other.
e. It is losing heat.
f. The temperature of the mixture will be closer to the high temperature. Each substance will gain / lose the
same amount of heat, but the cooler substance will change temperature significantly with the heat it gains
since it has a low specific heat. The hot substance will change temperature less since it takes more energy to
change its temperature because of its high specific heat.
6. Water
a. 4°C
b. The water molecules form a crystalline structure that takes up more space, which decreases the density.
c. More dense. Ice floats in water regardless of temperature.
d. More dense. Colder water, up to 4°C, is more dense than warmer water, which expands as it warms.
e. More dense. As water’s temperature drops from 4°C to 0°C, the crystalline structure begins to form, making it
less dense.
f. It is high… it takes a lot of energy to change the water’s temperature.
7. Methods of Heat Transfer
a.
b.
c.
d.
e.
f.
g.
h.
Conduction – collisions of molecules that transfer kinetic energy. Convection – energy is transferred in a
convection current due to density differences and because warmer substances expand while cooler ones are
more dense. Radiation – heat is radiated (given off) by all objects. The hotter it is, the more energy and the
shorter the wavelength.
Beaker A will cool faster because there is a greater temperature difference, so heat will flow faster.
Radiation
Convection Current
Radiation from the grill to the chicken, conduction within the chicken.
Range of wavelengths of energy that can be given off.
Shorter wavelengths = more energy.
The tile floor conducts heat better, whereas the bath mat acts as an insulator.
8. Latent Heat – Phase Change
a. No. The energy supplied by the hot plate is being used to convert the water from liquid to vapor.
b. It cools the surrounding air as it takes energy switch phases.
c. Energy is released to switch to a lower energy state of being a liquid.
d. Heat of vaporization is for a liquid to gas and vice versa. Heat
of fusion is the energy required per gram to change from solid
to liquid and vice versa.
e. No, the heat of vaporization is generally higher than the heat
D
of fusion, since it takes more energy to be a gas than a liquid
or solid.
f. The graph at right represents the heating curve of a substance
B
that starts as a solid below its freezing point.
i. ~58°C
C
ii. Liquid is vaporizing to become a gas, or gas is
A
condensing to become a liquid.
iii. AB, CD, or EF.
F
E