Energy changes

Question 1

If there is no charge…

Answer 1

There is no reaction

Question 2

Precise

Answer 2

How close the results are to each other

Question 3

Accurate

Answer 3

How close results are to the correct answer

Question 4

5 examples of exothermic reactions

Answer 4

Respiration
Combustion
Neutralisation of acids/alkalis
Thermit process
Reaction of metals with acids

Question 5

Thermit process

Answer 5

Displacement reaction of aluminium and ion oxide (produces molten heat)

Question 6

4 examples of endothermic reaction

Answer 6

Thermal decomposition
Photosynthesis
Some types of electrolysis
Sherbet

Question 7

What happens when making bonds ?

Answer 7

Release heat energy

Question 8

Exothermic reaction

Answer 8

Heat energy from reacting chemicals is transferred to surroundings to increase temperature of surroundings

Question 9

Endothermic reaction

Answer 9

Energy from surroundings is transferred to reacting chemicals to decrease temperature of surroundings

Question 10

Activation energy

Answer 10

All chemicals reactions need to get started and the minimum amount of energy reactants need to collide with each other and react

Question 11

Bond energy

Answer 11

Amount of energy needed to make or break bonds

Question 12

What charge does an exothermic reaction give?

Answer 12

Negative

Question 13

What charge does an endothermic reaction give?

Answer 13

Positive

Question 14

A sign of an endothermic reaction?

Answer 14

A fall in temperature in surroundings

Question 15

What do reaction profiles show?

Answer 15

The relative energy of the reactant and products in a reaction and how the energy changes over the course of the reaction

Question 16

The difference in height shows…

Answer 16

The overall energy change in reaction

Question 17

What will an endothermic reaction profile show?

Answer 17

Products are at higher energy than the reactants

Question 18

What will an exothermic reaction profile show?

Answer 18

Products are lower energy than the reactants

Question 19

What happens to the bonds in a chemical reaction?

Answer 19

Old bonds are broken and new bonds are formed

Question 20

Energy must be supplied ….

Answer 20

To break existing bonds (endothermic reaction)

Question 21

Energy is released …

Answer 21

When new bonds are formed (exothermic reaction)

Question 22

What can known bond energies be used to calculate?

Answer 22

The overall energy change

Question 23

How to calculate the overall energy change

Answer 23

Energies needed to break bonds in reactants - the energy released when new bonds formed in products

Question 24

What is an electrochemical?

Answer 24

Basic system made up of 2 different electrodes in contact with an electrolyte

Question 25

What does the chemical reactions between electrodes and electrolytes set up?

Answer 25

A charge difference between the electrodes

Question 26

What affects charge difference or voltage of a cell?

Answer 26

Different metals - react differently with the same electrolyte

Question 27

The bigger difference in reactivity of electrodes?

Answer 27

The bigger the voltage of cell

Question 28

Why might the electrolyte used in a cell affect the size of the voltage?

Answer 28

Different ions in solution will react differently with the metal electrodes

Question 29

What might happen over time to reacting particles?

Answer 29

Get used and turned into the products

Question 30

What happens if any one of the reactants get used up?

Answer 30

The reaction can't happen and so no electricity can be produced and products can't be reversed so cell can't be recharged

Question 31

How can a rechargeable cell be reveresed?

Answer 31

Connecting it to an external electric current

Question 32

What is a fuel cell?

Answer 32

An electrical cell that's supplied with a fuel and oxygen and uses energy from reaction between them to produce electrical energy efficiently

Question 33

What happens to the fuel when it enter the cell?

Answer 33

It becomes oxidised and sets up a potential difference within the cell?

Question 34

Example of a fuel cell

Answer 34

Hydrogen oxygen fuel cell

Question 35

What is the electrolyte often?

Answer 35

An acid

Question 36

Hydrogen oxygen fuel cell - redox reaction

Answer 36

1. Hydrogen goes into the anode compartment and oxygen goes into the cathode compartment 2. At the anode, hydrogen loses electrons to produce H+ ions (oxidation0 3. H+ in electrolyte move to cathode 5. At cathode, oxygen gains electrons form cathode and reacts with H+ ions from acidic electrolyte to make water (reduction) 6. Electrons flow through an external circuit from anode to cathode - an electric current 7. Overall reaction is hydrogen plus oxygen to give water

Question 37

What advantages do conventional fuels in vehicles have?

Answer 37

Finite supply

Question 38

Examples of getting cleaner energy

Answer 38

Batteries | hyrdogen-oxygen fuel cells

Question 39

Advantages of hydrogen oxygen fuel cell

Answer 39

- Don't have as many pollutants - Only by products are heat and water - Store more energy than batteries so less often recharged - Less expensive than fuel cells

Question 40

Why are batteries more polluting to dispose of than fuel cells?

Answer 40

Made of highly toxic metal compounds

Question 41

Disadvantages of hydrogen oxygen fuel cell

Answer 41

- Hydrogen is a gas so takes up more room than rechargeable battery - Hydrogen is explosive when mixed with air - Hydrogen fuel often made from hydrocarbons or by electrolysis of water that uses electricity

Question 42

How is exothermic reaction shown?

Answer 42

A rise in temperature in surroundings

Question 43

Advantages of fuel cells

Answer 43

Compact and lightweight Reliable Not very polluting High efficiency

Question 44

Factors affecting voltage of cell (4)

Answer 44

Different metals Bigger difference in reactivity of metals Type of electrolyte Battery

Question 45

Why might the difference in reactivity of metals affect the voltage?

Answer 45

Bigger voltage

Question 46

Why might the battery affect the voltage?

Answer 46

It is created by connecting 2+ cells together in series. Voltages of cells are combined to get bigger voltage overall

Question 47

What is the use of catalysts?

Answer 47

Increase reaction rates by lowering activation energy to increase chance that when particles collide they will have enough energy successfully react

Question 48

Energy transfer experiment

Answer 48

1. Put 0.25 mol/dm3 of hydrochloric acid ands sodium hydroxide in separate beakers 2. Place beakers in water bath set to 25 until they are both at the same temperature 3. Add HCL followed by NaOH to a polystyrene cup with lid 4. Take temperature of mixture every 30 seconds or until highest result starts to drop 5. Repeat steps 1-4 using 0.5 mol/dm3 and then 1 mol/dm3 of hydrochloric acid