3.3 Energy Change And Calculations

Question 1

What is released when substances burn?

Answer 1

Energy

Question 2

How can the energy released from a substance be measured?

Answer 2

Calorimetry

Question 3

What is calorimetry used for?

Answer 3

The energy values on the back of food packets

Question 4

What is simple calorimetry?

Answer 4

Heating water from the substance being burned with the temperature increase showing energy released

Question 5

How do you calculate energy transferred from a substance?

Answer 5

Q = M x C x ∆T

Energy transferred = Mass (of water) x Specific heat capacity x Change in temperature

Question 6

What are the two major sources of error in a practical when calculating heat loss?

Answer 6

Heat lost to surroundings is not accounted for

Incomplete combustion/reaction as lack of oxygen present

Question 7

What is used in industry to produce accurate food energy values?

Answer 7

Bomb calorimeter

Question 8

Why is a bomb calorimeter adapted for accurate energy values?

Answer 8

Constant supply of oxygen - no incomplete combustion
Temperature prove takes frequent readings - more accurate
Insulating jacket minimises heat loss
Magnetic stirrer allowing for constant stirring and consistent results

Question 9

What is exothermic?

Answer 9

Heat energy goes from the chemical reaction into the surroundings

Question 10

What is endothermic?

Answer 10

The heat energy goes from the surroundings into the chemical reaction

Question 11

What is the change of energy in exothermic? Why?

Answer 11

Negative

Energy is lost to the surroundings so the chemical reaction is cooler

Question 12

What is the change of energy is endothermic? Why?

Answer 12

Positive

Energy is taken into the chemical reaction from the surroundings so the chemical reaction is hotter

Question 13

When bonds are broken is it exo or endo?

Answer 13

Endothermic

Question 14

When bonds are made is it exo or endo?

Answer 14

Exothermic

Question 15

Describe the energy proportions in exothermic diagrams?

Answer 15

Energy released from forming bonds is greater than

Energy needed to break the existing bonds

Question 16

Describe the energy proportions in endothermic diagrams?

Answer 16

Energy needed to break the existing bonds is greater than

Energy released from forming new bonds

Question 17

What is the activation energy?

Answer 17

Where bonds are broken

Question 18

What do catalysts do?

Answer 18

Lower the activation energy

So the energy needed to break the bonds is lower

Question 19

What happens on a energy level diagram when a catalyst is used?

Answer 19

The curve upwards becomes shallower

Question 20

How do you calculate change in energy for a reaction?

Answer 20

Total energy needed to break all bonds in reactants
Take
Total energy released when new bonds are made in the products

Question 21

What will the question give you when calculating change in energy?

Answer 21

The bond energies
Eg
A C-H bond = +412kj/mol

Question 22

What will help you calculate change in energy?

Answer 22

The display formula to count the bonds

DON’T forget the balancing numbers when counting the bonds

Question 23

What is the issue with fossil fuels?

Answer 23

They are non-renewable and cause pollution

Question 24

What can be used as an alternative fuel?

Answer 24

Hydrogen

Question 25

Why is hydrogen used as an alternative fuel source?

Answer 25

Burns easily
Releases large amounts of energy
Produces only H2O

Question 26

What are the disadvantages of using hydrogen?

Answer 26

Difficult to acquire and store