Answers25-26 KCS18 Chemistry ICHeat

Heat Answers

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Heat that flows by conduction is the transfer of thermal energy between substances in contact. What must occur for this to happen?

A
The two systems must be the same temperature.
B
The two systems must not be touching each another.
C
One system must have higher kinetic energy than the other system.
D
The thermal energy of one system must be the same as the thermal energy of the other system.
2
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Which event is endothermic?

A
the burning of a match
B
the change of water vapor to a liquid
C
the combustion of propane gas
D
the melting of ice
3

Which answer defines exothermic reaction?

A
a process in which energy is released as heat
B
a process in which energy is absorbed as heat
C
a process in which energy is stored and released
D
a process in which energy is not present in a system
4

Which reaction is exothermic?

A
CH4 + 2O2 CO2 + 2H2O + 891 kJ
Option A
B
NH4NO3 + H2O + 25 kJ NH4+(aq) + NO3-(aq)
Option B
C
2H2O + 286 kJ 2H2 + O2
Option C
D
N2 + O2 + 181 kJ 2NO
Option D
5

A baker touches a pie right after taking it out of the oven. Which statement best explains why the pie feels hot?

A
Molecules in the skin move faster than molecules in the pie, so heat is transferred to the pie.
B
Molecules in the pie move faster than molecules in the skin, so heat is transferred to the skin.
C
Molecules in the skin move faster than molecules in the pie, so heat is transferred to the skin.
D
Molecules in the pie move faster than molecules in the skin, so heat is transferred to the pie.
6

Two samples of carbon come into contact. A heat transfer will occur between sample A and sample B. What must be true for heat to transfer from sample A to sample B?

A
The average kinetic energy of A is greater than that of B.
B
The average kinetic energy of B is greater than that of A.
C
The average kinetic energy of both samples is equal.
D
The average kinetic energy does not determine the direction of heat transfer.
7

The temperature of a sample of liquid water changes from 50°C to 30°C. Which statement best explains the change that must happen at the molecular level?

A
The molecules move more quickly and their average kinetic energy increases.
B
The molecules move more slowly and their average kinetic energy decreases.
C
The molecules move more quickly and their average kinetic energy decreases.
D
The molecules move more slowly and their average kinetic energy increases.
8

Which statement about exothermic reactions is accurate?

A
As reactants form products, the potential energy decreases.
B
As reactants form products, the potential energy increases.
C
Thermal energy is transferred from the product to the reacting substances.
D
Thermal energy is transferred from the surroundings to the reacting substances.
9

The diagram below shows the temperature dropping from 80°C to 20°C.Molecules that have longer arrows are moving faster. Which statement describes what is happening in this system?

Question illustration
A
Molecules vibrate more as temperature decreases.
B
Temperature is not related to the average kinetic energy of a system.
C
Kinetic energy decreases as temperature decreases.
D
There is no change in average kinetic energy between these two systems.
10

Two different gases are stored in separate closed containers. If both gases have a temperature of 50°C, which statement is true?

A
The thermal energies of gas molecules in the two containers are unrelated.
B
The gas molecules in both containers will absorb heat from the surroundings.
C
The molecules in one gas will transfer energy to the molecules in the other gas.
D
The gas molecules in both containers have the same average kinetic energy.

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