C7: Energy Changes

Question 1

What do we call the elements/compounds that react together in a chemical reaction?

Answer 1

The reactants

Question 2

What do we call the elements/compounds that are formed in a chemical reaction?

Answer 2

The products

Question 3

In an exothermic reaction, where is energy transferred from and to?

Answer 3

Energy is transferred from the reacting chemicals into the surroundings

Question 4

In an endorthermic reaction, where is energy transferred from and to?

Answer 4

Energy is transferred from the surroundings into the reacting chemicals

Question 5

In exothermic reactions, does the overall temperature of the surroundings increase or decrease?

Answer 5

The overall temperature of the surroundings increases

Question 6

In endothermic reactions, does the overall temperature of the surroundings increase or decrease?

Answer 6

The overall temperature of the surroundings decreases

Question 7

What is an example of an exothermic reaction in our everyday lives?

Answer 7

Hand-warmer packets

Question 8

What is an example of an endothermic reaction in our everyday lives?

Answer 8

Sports injury ice packs

Question 9

What is an example of an exothermic reaction?

Answer 9

Burning of fuels

Question 10

What is an example of an endothermic reaction?

Answer 10

Decomposition reaction

Question 11

When drawing a reaction profile, what goes on the Y-axis?

Answer 11

The overall energy

Question 12

When drawing a reaction profile, what goes on the X-axis?

Answer 12

Progress of reaction

Question 13

What is the activation energy in a reaction?

Answer 13

The minimum amount of energy needed for a chemical reaction to occur

Question 14

In an exothermic reaction, is the overall energy change positive or negative?

Answer 14

Negative

Question 15

In an endothermic reaction, is the overall energy change positive or negative?

Answer 15

Positive

Question 16

When drawing a reaction profile, should the arrows be double sided arrows?

Answer 16

No they must only be single sided arrows with the arrow leading away from the reactants

Question 17

How do you figure out the overall energy change of a reaction?

Answer 17

Total amount of energy needed to break the bonds

TAKE OFF

Total amount of energy needed to make the bonds

EQUALS

Total energy change of the reaction

Question 18

If a chemical reaction has a negative overall energy change is it exothermic or endothermic?

Answer 18

Exothermic

Question 19

If a chemical reaction has a positive overall energy change is it exothermic or endothermic?

Answer 19

Endothermic

Question 20

If a chemical reaction has an overall energy change of 0KJ/mol is it exothermic or endothermic?

Answer 20

Neither exothermic or endothermic

Question 21

What unit is the overall energy change of a reaction in?

Answer 21

KJ/mol

Question 22

How do chemical cells produce electricity?

Answer 22

Chemical cells produce electricity through chemical reactions

Question 23

What is the difference between a battery and a cell?

Answer 23

A battery is two or more cells put together so a higher voltage can be achieved

Question 24

Why are rechargeable cells rechargeable?

Answer 24

Rechargeable cells can be recharged as the chemical reactions inside the cells can be reversed when an external electrical current is supplied

Question 25

Why can non-rechargeable cells not be recharged?

Answer 25

As the chemical reactions inside the cells stop when one of the reactants has been used up (they are not reversible)

Question 26

Order these 3 types or cells from MOST EXPENSIVE to LEAST EXPENSIVE: Rechargeable cells, Non-Rechargeable cells, Fuel cells

Answer 26

1) Fuel cells 2) Rechargeable cells 3) Non-rechargeable cells

Question 27

What is 1 advantage and 1 disadvantage of non-rechargeable cells?

Answer 27

Advantage: They are much easier to make than rechargeable and fuel cells (also the cheapest out of the 3) Disadvantage: They cannot be recharged

Question 28

What is 1 advantage and 1 disadvantage of rechargeable cells?

Answer 28

Advantage: They can be recharged Disadvantage: They can take a lot of time to recharge (also more expensive than non-rechargeable cells)

Question 29

What is 1 advantage and 1 disadvantage of fuel cells?

Answer 29

Advantages: The only waste product that fuel cells produce is water Disadvantage: It is the most expensive of the 3 cells

Question 30

What is the most common type of fuel cell?

Answer 30

Hydrogen-oxygen fuel cells

Question 31

What are 3 advantages and 3 disadvantages of hydrogen-oxygen fuel cells?

Answer 31

Advantages: - The only waste product produces is water - Only requires hydrogen and oxygen to use - Lasts longer than bateries Disadvantages: - Is relatively expensive to setup - Uses hydrogen which is flammable and therefore dangerous to store - The hydrogen used requires more space to store than fossil fuels or batteries

Question 32

What is different about a fuel cell setup than a usual electrolysis setup?

Answer 32

- The cathode is the positive electrode (rather than negative as usual) and the anode is the negative electrode (rather than positive as usual) - The electrolyte is positioned in between the two electrodes, rather than the two electrodes being dipped inside the electrolyte

Question 33

What are the electrodes in fuel cells made of?

Answer 33

Carbon

Question 34

Explain the process of the chemical reaction that happens in a fuel cell?

Answer 34

1) Hydrogen molecules enter the cell from the left, and are then oxidised at the anode as they lose one electron to become a hydrogen ion 2) The electrons that have been displaced at the anode travel along the wire to the cathode, whilst the hydrogen ions pass from the anode to the cathode through the electrolyte 3) Oxygen then enters through the right of the fuel cell to the cathode, in which it combines with the hydrogen ions to create water (note that it takes 2 sets of hydrogen ions to combine with each set of oxygen ions, as 2 hydrogen ions pair up with 1 oxygen atom)

Question 35

What do fuel cells do?

Answer 35

Fuel cells convert chemical energy from a chemical reaction into electricity

Question 36

Does BREAKING BONDS require energy or release energy?

Answer 36

Require energy

Question 37

What is an example of a non-rechargeable battery?

Answer 37

An alkaline battery

Question 38

What is the acronym for the reactivity series and which element does each word represent?

Answer 38

**P**olite - **P**ottasium **S**potted - **S**odium **L**eopard - **L**ithium **C**an - **C**alcium **M**eet - **M**agnesium **A**ffectionate - **A**luminium **Z**ebra - **Z**inc **I**nto - **I**ron **T**ender - **T**in **L**oving - **L**ead **C**are - **C**opper **S**ingle - **S**ilver **G**irls - **G**old **P**lease - **P**latinum

Question 39

Where does hydrogen fit into the reactivity series?

Answer 39

In-between lead and copper

Question 40

Where does carbon fit into the reactivity series?

Answer 40

In-between aluminium and zinc

Question 41

What is an exothermic reaction?

Answer 41

A reaction that releases thermal energy into the surroundings

Question 42

What is an endothermic reaction?

Answer 42

A reaction that takes in thermal energy from the surroundings

Question 43

What is the half equation that takes place at the anode in fuel cells?

Answer 43

H2 ---> 2H+ + 2e-

Question 44

How does a fuel cell generate electricity?

Answer 44

1) The hydrogen atoms are oxidised at the anode, causing 2 electrons to be displaced and left at the anode 2) This causes a potential difference in the circuit due to the difference in charge between the two electrodes 3) This potential difference drives the electrons around the circuit, generating electricity