Answers25-26 KCS18 Chemistry ICHeat

Heat Answers

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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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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.
3

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
4

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
5

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
6

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.
7

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.
8

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.
9

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.
10

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.

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