Energy Changes

Question 1

What is an exothermic reaction?

Answer 1

Energy is transferred to the surroundings (exits)

Question 2

What happens to the temperature of an
exothermic reaction?

Answer 2

Temperature increases

Question 3

What is an endothermic reaction?

Answer 3

Energy is taken in from the surroundings

Question 4

What happens to the temperature of an
endothermic reaction?

Answer 4

Temperature decreases

Question 5

Give examples of exothermic reactions

Answer 5

Combustion
Neutralisation
Respiration
Oxidation reactions

Question 6

Give every day uses of exothermic
reactions

Answer 6

Self-heating cans
Hand warmers

Question 7

Give examples of endothermic reactions

Answer 7

Thermal decomposition
Photosynthesis
Citric acid and sodium hydrogen carbonate (sherbet)

Question 8

Give every day uses of endothermic
reactions

Answer 8

Sports injury packs

Question 9

What is the energy of the products
compared to reactants in an exothermic
reaction?

Answer 9

Less

Question 10

What is the energy of the products
compered to reactants in an endothermic
reaction?

Answer 10

More

Question 11

What is activation energy ?

Answer 11

Minimum energy that particles must have for a reaction
to occur

Question 12

What does a reaction profile show?

Answer 12

It is a graphical representation of energy vs reaction progression.

It allows us to see how the energy of the reactants and products change over a reaction.

It should always include the activation energy (represented as a hump going from the reactants).

Question 13

Draw a reaction profile for an exothermic
reaction

Question 14

Draw a reaction profile for an endothermic
reaction

Question 15

What does a catalyst do to the activation
energy

Answer 15

Lowers it, by providing an alternative path

Question 16

Draw a reaction profile for a reaction with
a catalyst

Question 17

What is needed to break a bond

Answer 17

Energy

Question 18

REQUIRED PRACTICAL: How can you
investigate variables that affect temperature changes in reacting solutions such as:
Acid + metal
Acid + metal carbonate
Acid + base
Displacement reactions
Note this method is very generic as depends what the independent/ dependent variables are.

Answer 18

1. Use an insulating beaker, add an appropriate volume
   of liquid using a measuring cylinder.
2. Measure the initial temperature and record this.
3. Add a set mass (e.g. 1g) of the other reactant and
   stir
4. Measure the highest temperature or measure the
   temperature after a set time and record this.
5. Calculate the temperature difference
6. Repeat with same volume of liquid but different
   masses or different reactants (depends what
   investigating)

Question 19

What type of process is bond breaking

Answer 19

Endothermic

Question 20

What is given out when a bond is made

Answer 20

Energy

Question 21

What type of process is bond making

Answer 21

Exothermic

Question 22

Why is a reaction endothermic overall in
terms of bonds breaking and making

Answer 22

More energy is taken in during bond breaking than is
given out during bond making

Question 23

Why is a reaction exothermic overall in
terms of bonds breaking and making

Answer 23

More energy is given out during bond making than is
taken in during bond breaking

Question 24

How can you calculate the overall energy
change in a reaction

Answer 24

Sum of bonds broken - sum of bonds made
AKA (reactants – products)

Question 25

Here is an example calculation

Question 26

What do cells contain

Answer 26

Chemicals which react to produce electricity

Question 27

What is the voltage of a cell dependent on

Answer 27

Type of electrode (different metals) Electrolyte Concentration of electrolyte Temperature

Question 28

How can a simple cell be made

Answer 28

Connecting two different metals (have different reactivity) Putting these in contact with an electrolyte. The bigger the difference in reactivity between the two metals the larger the voltage.

Question 29

What is an electrolyte

Answer 29

A liquid that contains ions which react with the electrode

Question 30

How does the voltage produced in a cell represent the reactivity of the metals?

Answer 30

Larger the positive voltage, the more reactive the metal

Question 31

What is a battery

Answer 31

Two or more cells connected together in series to provide a greater voltage. E.g. connect two 1.5V cells in series to produce a 3.0V battery.

Question 32

What are non-rechargeable cells and batteries

Answer 32

The chemical reaction is irreversible Stops when one of the reactants have been used up Alkaline batteries are non-rechargeable

Question 33

What are rechargeable cells and batteries

Answer 33

Chemical reactions are reversible When an external electrical circuit is supplied

Question 34

What is a fuel cell

Answer 34

Supplied by an external source of fuel (e.g.Hydrogen and Oxygen/air) The fuel is oxidised electrochemically within the fuel cell to produce a potential difference.

Question 35

How are fuel cells and chemical cells different?

Answer 35

Fuel cells produce a voltage continusouly as long as they have: A supply of a suitable fuel Oxygen Fuel cells oxidise the fuel electrochemically (in chemical cells the fuel is burned)

Question 36

What is a common fuel used in a fuel cell

Answer 36

Hydrogen

Question 37

What solutions can be used as the electrolyte in a hydrogen fuel cell

Answer 37

An alkali e.g. potassium hydroxide An acid e.g. hydrochloric acid

Question 38

If the electrolyte is an alkali What happens at the negative electrode (anode)? Write a half equation to represent this.

Answer 38

Hydrogen reacts with hydroxide ions to produce water. This produces electrons H2 + 2OH- → 2e- + 2H2O

Question 39

If the electrolyte is an alkali What happens at the positive electrode (Anode)?

Answer 39

Oxygen reacts with water to produce hydroxide ions. This uses up the electrons (produced from anode). O2 + 4e- + 2H2O → 4OH-

Question 40

If the electrolyte is an acid What happens at the positive electrode (cathode)?

Answer 40

Oxygen is reduced (gains electrons) O2 + 4H+ + 4e-→ 2H2O

Question 41

If the electrolyte is an acid What happens at the negative electrode (cathode)? Write a half equation to represent this.

Answer 41

H2 → 2H+ + 2e- Hydrogen is oxidised (loses electrons)

Question 42

What is the overall equation for the hydrogen-fuel cell?

Answer 42

2H2 + O2 → 2H2O Hydrogen + oxygen → water (In the alklai: the 4OHions, 4e- and 2H2O molecules cancel out)

Question 43

Name advantages for a hydrogen fuel cell

Answer 43

* Coventional fuels are finite so saves resources, * Does not produce pollutants (no CO2 produced) * Only by products are water and heat * Faster to refuel (than recharging) * Can travel further * Can be renewable if hydrogen is made by electrolysis using renewable energy

Question 44

Name disadvantages for a hydrogen fuel cell

Answer 44

* Hydrogen is made from fossil fuels * Difficult to store * Hydrogen is made from non-renewable resources * Hydrogen is explosive so safety issues * Costs more to refuel (than recharging) * Costs more to manufacture * Not many hydrogen filling stations