Answers SS - TX - Chemistry BWriting and Balancing Chemical Equations

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

Molecules in the skin move faster than molecules in the pie, so heat is transferred to the pie.

Molecules in the pie move faster than molecules in the skin, so heat is transferred to the skin.

Molecules in the skin move faster than molecules in the pie, so heat is transferred to the skin.

Molecules in the pie move faster than molecules in the skin, so heat is transferred to the pie.

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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.

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 reaction is exothermic?

CH4 + 2O2 CO2 + 2H2O + 891 kJ

NH4NO3 + H2O + 25 kJ NH4+(aq) + NO3-(aq)

2H2O + 286 kJ 2H2 + O2

N2 + O2 + 181 kJ 2NO

Which event is endothermic?

the burning of a match

the change of water vapor to a liquid

the combustion of propane gas

the melting of ice

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

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.

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.

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

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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