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
11

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.
12

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
13

In what type of reaction or process does heat flow into the system?

A
combustion
B
exothermic
C
condensation
D
endothermic
14

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.
15

An ice cube is placed on a kitchen counter. Which best describes heat flow in this situation?

A
Heat flows from the ice to the counter, causing the molecules in the counter to move more quickly.
B
Heat flows from the ice to the counter, causing the molecules in the counter to move more slowly.
C
Heat flows from the counter to the ice, causing the molecules in the counter to move more quickly.
D
Heat flows from the counter to the ice, causing the molecules in the counter to move more slowly.
16

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
17

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.
18

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.
19

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
20

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.
21

A hot metal plate at 150°C has been placed in air at room temperature. Which event would most likely take place over the next few minutes?

A
Molecules in both the metal and the surrounding air will start moving at lower speeds.
B
Molecules in both the metal and the surrounding air will start moving at higher speeds.
C
The air molecules that are surrounding the metal will slow down, and the molecules in the metal will speed up.
D
The air molecules that are surrounding the metal will speed up, and the molecules in the metal will slow down.
22

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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