AnswersTX-Chemistry BUnit Test

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1
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What is thermal energy?

A
the average overall volume of a system
B
the total number of molecules in a system
C
the kinetic energy of particles in a system
D
the measure of temperature in a system
2
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The temperature of a gas is increased. Which statement best explains the effect that this has on the motion of gas particles?

A
The average kinetic energy decreases, and the particles stop colliding.
B
The average kinetic energy increases, and the particles stop colliding.
C
The average kinetic energy decreases, and the particles collide less frequently.
D
The average kinetic energy increases, and the particles collide more frequently.
3

How does the potential-energy diagram for a reaction indicate whether the reaction is endothermic or exothermic?

A
An endothermic reaction has reactants that are lower in energy than products because energy is absorbed to form the products.
B
An endothermic reaction has reactants that are higher in energy than products because energy is released to form the products.
C
An exothermic reaction has reactants that are lower in energy than products because energy is released to form the products.
D
An exothermic reaction has reactants that are higher in energy than products because energy is absorbed to form the products.
4

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.
5

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.
6

A student touches a freshly baked cake that was taken out of the oven. Which best explains why the cake feels hot?

A
Molecules in the skin are moving faster than molecules in the cake.
B
Molecules in the cake are moving faster than molecules in the skin.
C
The kinetic energy of molecules in the cake is more than the energy in the baking tray.
D
The kinetic energy of molecules in the baking tray is more than the energy in the cake.
7

Iron reacts with oxygen in a chemical hand-warmer. How should this reaction be categorized?

A
as an exothermic process because it releases heat
B
as an endothermic process because it releases heat
C
as an exothermic process because it absorbs heat
D
as an endothermic process because it absorbs heat
10

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

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Heat Answers — TX-Chemistry B