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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?

Molecules vibrate more as temperature decreases.

Temperature is not related to the average kinetic energy of a system.

Kinetic energy decreases as temperature decreases.

There is no change in average kinetic energy between these two systems.

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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?

The average kinetic energy decreases, and the particles stop colliding.

The average kinetic energy increases, and the particles stop colliding.

The average kinetic energy decreases, and the particles collide less frequently.

The average kinetic energy increases, and the particles collide more frequently.

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

Molecules in the skin are moving faster than molecules in the cake.

Molecules in the cake are moving faster than molecules in the skin.

The kinetic energy of molecules in the cake is more than the energy in the baking tray.

The kinetic energy of molecules in the baking tray is more than the energy in the cake.

Which answer defines exothermic reaction?

a process in which energy is released as heat

a process in which energy is absorbed as heat

a process in which energy is stored and released

a process in which energy is not present in a system

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

An endothermic reaction has reactants that are lower in energy than products because energy is absorbed to form the products.

An endothermic reaction has reactants that are higher in energy than products because energy is released to form the products.

An exothermic reaction has reactants that are lower in energy than products because energy is released to form the products.

An exothermic reaction has reactants that are higher in energy than products because energy is absorbed to form the products.

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?

The average kinetic energy of A is greater than that of B.

The average kinetic energy of B is greater than that of A.

The average kinetic energy of both samples is equal.

The average kinetic energy does not determine the direction of heat transfer.

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?

The molecules move more quickly and their average kinetic energy increases.

The molecules move more slowly and their average kinetic energy decreases.

The molecules move more quickly and their average kinetic energy decreases.

The molecules move more slowly and their average kinetic energy increases.

What is thermal energy?

the average overall volume of a system

the total number of molecules in a system

the kinetic energy of particles in a system

the measure of temperature in a system

Which statement about exothermic reactions is accurate?

As reactants form products, the potential energy decreases.

As reactants form products, the potential energy increases.

Thermal energy is transferred from the product to the reacting substances.

Thermal energy is transferred from the surroundings to the reacting substances.

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?

Molecules in both the metal and the surrounding air will start moving at lower speeds.

Molecules in both the metal and the surrounding air will start moving at higher speeds.

The air molecules that are surrounding the metal will slow down, and the molecules in the metal will speed up.

The air molecules that are surrounding the metal will speed up, and the molecules in the metal will slow down.

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