Energy Changes

Question 1

What is an exothermic reaction

Answer 1

A reaction that transfers energy to the surroundings, usually by heating
Shown by rise in temperature

Question 2

Examples of exothermic reactions

Answer 2

Combustion (burning fuels)
Neutralisation reactions
Oxidation reactions

Question 3

Uses of exothermic reactions in everyday life

Answer 3

Hand warmers

Self heating cans of hot chocolate and coffee

Question 4

What is an endothermic reaction

Answer 4

A reaction which takes in energy from surroundings

Shown by fall in temperature

Question 5

Examples of endothermic reactions

Answer 5

Citric acid with sodium hydrocarbonate

Thermal decomposition

Question 6

Uses of endothermic reactions in everyday life

Answer 6

Sports injury ice packs

Question 7

How do you test the effect of acid concentration on the energy released in a neutralisation reaction between HCL and NaOH (required practical)

Answer 7

Put 25cm^3 of 0.25 mol/dm^3 HCL and NaOH in separate beakers
Place beakers in a water bath at 25 degrees until both are at same temperature
Add both liquids to a polystyrene cup with lid
Take the temperature of mixture every 30 seconds and record highest temperature
Repeat using 0.5mol/dm^3 and then 1 oml/dm^3 of HCL and record temperatures

Question 8

What is the biggest problem with energy measurement experiments, and how can this be reduced

Answer 8

The problem is energy is often lost to the surroundings and this isn’t recorded
Can be reduced by putting polystyrene cup into a beaker of cotton wool to give more insulation and put lid on cup to reduce energy loss by evaporation

Question 9

What is a reaction profile

Answer 9

A diagram that shows the relative energies of the reactants and products in a reaction and how the energy changes over the course of the reaction

Question 10

What is activation energy and what does it show

Answer 10

It is the minimum amount of energy the reactants need to collide with each other and react.
The greater it is, the more energy needed to start the reaction, this has to be supplied eg by heating the reaction mixture

Question 11

What does an exothermic reaction profile show

Answer 11

The difference in height represents the overall energy change in the reaction (energy given out) per mole
The initial rise in energy represents the energy needed to start the reaction (activation energy)

Question 12

What does the endothermic reaction profile show

Answer 12

The products are at a higher rate than the reactants (absorbs energy)
The difference in height represents the overall energy change during the reaction (energy taken in)

Question 13

Energy must be supplied to break existing bonds, is bond breaking an endothermic process or exothermic

Answer 13

Endothermic

Question 14

Is bond formation exothermic or endothermic and why

Answer 14

Exothermic because energy is released

Question 15

How do you calculate the overall energy change in bond energy calculations

Answer 15

Sum of energies needed to break bonds in the reactants minus the energy released when new bonds are formed

Question 16

What is aN electrochemical cell

Answer 16

A basic system made up of two different electrodes in contact with an electrolyte

Question 17

Why are the two electrodes metal in a electrochemical cell

Answer 17

So they can conduct electricity

Question 18

What is an electrolyte in an electrochemical cell

Answer 18

It is a liquid that contains ions which react with the electrodes

Question 19

What do the chemical reactions between the electrodes and the electrolyte do in an electrochemical cell

Answer 19

They set up a charge difference between the electrodes

Question 20

Why are the electrodes connected by a wire in an electrochemical cell

Answer 20

A charge is able to flow between them so electricity is produced

Question 21

Why is a voltmeter connected between the two electrodes in an electrochemical cell

Answer 21

To measure the voltage of the cell

Question 22

What factor causes the charge difference of voltage of a cell to change

Answer 22

The way the different metals react differently with the same electrolyte

Question 23

True or false the bigger the difference in reactivity of the electrodes, the bigger the voltage of the cell

Answer 23

True

Question 24

How is a battery formed and how is it’s voltage larger

Answer 24

Connecting two or more cells together in series

The voltage of the cells in a battery are combined so there is a bigger voltage overall