5.1 Energy Changes in Chemical and Nuclear Reactions

Question 1

thermochemistry

Answer 1

the study of the energy changes that accompany physical or chemical changes in matter

Question 2

energy

Answer 2

the ability to do work; SI units
joules (J)

Question 3

work

Answer 3

the amount of energy transferred by
a force over a distance; SI units joules (J)

Question 4

potential energy

Answer 4

the energy of a body or system due to its position or composition

Question 5

kinetic energy

Answer 5

the energy of an object due to its motion

Question 6

thermal energy

Answer 6

the total quantity of kinetic and potential energy in a substance

Question 7

heat

Answer 7

the transfer of thermal energy from
a warm object to a cooler object

Question 8

temperature

Answer 8

a measure of the average
kinetic energy of entities in a substance

Question 9

chemical system

Answer 9

a group of reactants and products being studied

Question 10

surroundings

Answer 10

all the matter that is not part of the system

Question 11

open system

Answer 11

a system in which both matter and energy are free to enter and leave the system

Question 12

closed system

Answer 12

a system in which energy can enter and leave the system, but matter cannot

Question 13

isolated system

Answer 13

an ideal system in which neither matter nor energy can move in or out

Question 14

exothermic

Answer 14

releasing energy to the surroundings

Question 15

endothermic

Answer 15

absorbing energy from the surroundings

Question 16

The products of an exothermic reaction have _____ potential energy (and _______ bonds on average) than the reactants.

Answer 16

lower; stronger

Question 17

The products of an endothermic reaction have _____ potential energy (and ______ bonds on average) than the reactants.

Answer 17

higher; weaker

Question 18

In an exothermic reaction, energy is written as a ______

Answer 18

product

Question 19

In an endothermic reaction, energy is written as a ______

Answer 19

reactant

Question 20

fusion

Answer 20

the process of combining two or more nuclei of low atomic mass to form a heavier, more stable nucleus

Question 21

fission

Answer 21

the process of using a neutron to split a nucleus of high atomic mass into two nuclei with smaller masses

Question 22

For each of the following, describe which is greater, the potential energy or the kinetic energy.
(a) a stick of dynamite prior to exploding

Answer 22

(a) A stick of dynamite prior to exploding has greater potential energy than kinetic energy.

Question 23

For each of the following, describe which is greater, the potential energy or the kinetic energy.
(b) a space shuttle before launch

Answer 23

(b) A space shuttle before launch has greater potential energy than kinetic energy.

Question 24

For each of the following, describe which is greater, the potential energy or the kinetic energy.
(c) the soot rising above a campfire

Answer 24

(c) The soot rising above a campfire has greater kinetic energy than potential energy.

Question 25

For each of the following, describe which is greater, the potential energy or the kinetic energy.
(d) the chemicals inside a new battery

Answer 25

(d) The chemicals inside a new battery have greater potential energy than kinetic energy.

Question 26

For each of the following, identify whether the
reaction process is exothermic or endothermic.

(a) water evaporating into steam

Answer 26

(a) Water evaporating into steam is an endothermic process.

Question 27

For each of the following, identify whether the
reaction process is exothermic or endothermic.

(b) a candle burning

Answer 27

(b) A candle burning is an exothermic reaction.

Question 28

For each of the following, identify whether the
reaction process is exothermic or endothermic.

(c) the combustion of gasoline

Answer 28

c) The combustion of gasoline is an exothermic reaction.

Question 29

For each of the following, identify whether the
reaction process is exothermic or endothermic.

(d) the melting of ice

Answer 29

(d) The melting of ice is an endothermic process.

Question 30

For each of the following, identify whether the
reaction process is exothermic or endothermic.

(e) the splitting of a nitrogen molecule, N2, into
individual atoms

Answer 30

(e) The splitting of a nitrogen molecule, N2, into individual atoms is an endothermic reaction.

Question 31

For each of the following, identify whether the
reaction process is exothermic or endothermic.

(f) dissolving barium hydroxide, Ba(OH)2, in water and observing a temperature decrease in the surroundings

Answer 31

(f) Dissolving barium hydroxide, Ba(OH)2, in water and observing a temperature decrease in the surroundings is an endothermic process.

Question 32

Distinguish between heat, thermal energy, and
temperature.

Answer 32

Heat is the transfer of thermal energy from a warm object to a cooler object.

Thermal Energy is the total potential and kinetic energy of a substance. The quantity of thermal energy of a substance depends on how fast its entities (such as atoms, ions, or molecules) are moving.

Temperature is a measure of the average kinetic energy of the entities in a substance. As the average kinetic energy of the substance’s entities increases, the temperature of the substance increases.

When a hot burner heats a pot of water on the stove, thermal energy is transferred from the hot material of the pot to the cooler water inside the pot.

As water gains thermal energy, its kinetic energy increases and some of its particles move faster, so the temperature of the water increases.

Question 33

Compare and contrast nuclear fission and fusion.

Answer 33

Fission is a nuclear reaction in which a neutron collides with a nucleus of high atomic mass
and splits it into nuclei with smaller masses.

Fusion is a nuclear reaction in which two or more
nuclei of low atomic mass combine to form a heavier nucleus.