Chapter Ten

Question 1

Where is chemical energy stored

Answer 1

In between the bonds between atoms and molecules

Question 2

Chemical energy results from

Answer 2

• Attraction between e- and p+ in atoms
• Repulsions between nuclei
• Repulsions between e-
• Movement of electrons
• Vibrations and rotations around bonds

Question 3

What is the SI unit for energy

Answer 3

Joule

Question 4

Additional SI units for energy

Answer 4

• Kilojoules
• Megajoules

Question 5

What is the relationship between Kj, Mj and J

Answer 5

1 MJ = 1000kJ = 1 000 000 J

Question 6

Law of conservation of energy

Answer 6

Energy cannot be created or destroyed but it can change forms

Question 7

System

Answer 7

The chemical reaction

Question 8

Surroundings

Answer 8

Usually regarded as everything that is not the chemical reaction

Question 9

Energy leaves the… into the … or leaves the … into the …

Answer 9

• Surroundings, system
• System, surroundings

Question 10

What determines whether energy is released or absorbed

Answer 10

The relative energies of the bonds within the reactants and products

Question 11

Will separated particles have more or less energy than when they were together

Answer 11

More

Question 12

What happens to the bond when energy is absorbed

Answer 12

The bond breaks

Question 13

What happens to energy when bonds form

Answer 13

Energy is released

Question 14

What forms does energy take

Answer 14

• Heat
• Light
• Electricity
• Kinetic

Question 15

Endothermic reactions

Answer 15

• Energy enters the system
• The total chemical energy of the reactants is less than the products
• Absorbs heat from surroundings so the environment becomes cooler

Question 16

Exothermic reactions

Answer 16

• Energy is released into the surroundings
• Total chemical energy or reactants is more than the products
• All combustion reactions give off heat energy to the surroundings

Question 17

Changes of state

Answer 17

• Phase changes
• Physical changes but still involves energy being released/absorbed

Question 18

Heat taken from environment =

Answer 18

Endothermic

Question 19

Heat released to environment =

Answer 19

Exothermic

Question 20

Enthalpy (H)

Answer 20

The stored chemical energy of a substance

Question 21

Enthalpy change/ heat of reaction (ΔH)

Answer 21

The exchange of heat between the system and its surroundings

Question 22

Enthalpy change in endothermic reactions

Answer 22

• System has gained energy so ΔH is positive
• ΔH > 0

Question 23

Enthalpy change in exothermic reactions

Answer 23

• System has lost energy so ΔH is negative
• ΔH < 0

Question 24

Where are the enthalpy changes written in thermochemical equations

Answer 24

To the right of the equation

Question 25

What units is enthalpy measured in

Answer 25

kJmol^-1

Question 26

How do you compare enthalpy changes

Answer 26

Compare equal quantities of the substance

Question 27

How is ΔH effected by reversing a chemical reaction

Answer 27

Reversing a chemical reaction changes the sign but not the magnitude of the ΔH (- or +)

Question 28

Activation energy

Answer 28

The energy required to break the bonds of reactants so that a reaction can proceed