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GCSE Chemistry > Energy Changes > Flashcards

Energy Changes Flashcards

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1
Q

True or false, energy is stored in chemical bonds

A

True

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2
Q

Different chemical bonds hold different amounts of …

A

Energy

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3
Q

What type of reaction releases thermal energy to the surroundings

A

Exothermic

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4
Q

In an exothermic reaction does the temperature of surroundings increase

A

Yes because (thermal) energy is released

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5
Q

What is an endothermic reaction

A

A reaction that takes in thermal energy from its surroundings

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6
Q

What happens to the temperature of the surroundings in an endothermic reaction and why

A

Decreases
Thermal energy is taken in

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7
Q

In an endothermic reaction do the reactants or products have more energy

A

Product as energy is taken in from surroundings

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8
Q

In an exothermic reaction do the reactants or products have more energy

A

Reactants as energy is released to the surroundings

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9
Q

What is meant by activation energy

A

Minimum amount of energy the reactant particles require in order to collide with each other and react

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10
Q

On reactant profile diagrams what’s on the x axis

A

Progress of reaction

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11
Q

In reaction profile diagrams what’s in the y axis

A

Energy

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12
Q

In a reaction profile diagram where is the activation energy

A

From the reactants to the peak of the curve

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13
Q

What represents the energy change in a reaction profile diagram

A

Line between reactants and products

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14
Q

Does breaking bonds release or require energy

A

Require

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15
Q

Is breaking bonds exothermic or endothermic and why

A

Endothermic because it requires energy (energy is taken in)

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16
Q

What is bond energy

A

The amount of energy required to break one mole of a particular covalent bond

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17
Q

What can be defined as the amount of energy required to break one mole of a particular covalent bond

A

Bond energy

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18
Q

If the total bond energy of the reaction is negative is it exothermic or endothermic and why

A

Exothermic-
Energy is being lost hence the negative

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19
Q

Is forming bonds endothermic or exothermic and why

A

Exothermic as it releases energy

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20
Q

Equation used to calculate overall energy change of reaction

A

Energy of reactants- energy of products
(Energy of bonds broken- energy of bonds formed)

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21
Q

What type of reaction produces a negative energy change

A

Exothermic

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22
Q

During a chemical reaction must the bonds of the products be broken or formed

A

Formed

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23
Q

Exothermic reactions transfer energy to their surroundings in the form of…

A

Heat

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24
Q

Examples of exothermic reactions

A

Combustion (burning)- where fuels are burnt by reacting with oxygen and release energy
Neutralisation reactions between acids and bases
Oxidation reactions

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25
Q

What do (electrochemical) cells use to produce electricity

A

Chemical reactions

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26
Q

3 factors that affect voltage of a cell

A

Metals used as electrode (greater difference in reactivity between metals means higher voltage)
Type and concentration of electrolyte
Conditions e.g temperature

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27
Q

If there is a higher difference in reactivity between the 2 metals used in the electrodes does this increase or decrease voltage of the cell

A

Increase

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28
Q

Out of rechargeable and non-rechargeable cells for which one can the chemical reaction be reversed

A

Rechargeable

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29
Q

Why can rechargeable cells and batteries be recharged

A

The chemical reaction is reversible when an external electrical current is supplied

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30
Q

2 examples of devices that contain rechargeable batteries

A

Laptop/ mobile phone

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31
Q

In non-rechargeable cells and batteries when does the chemical reaction stop

A

When one of the reactants has been used up

32
Q

2 examples of what non-rechargeable batteries are used for

A

Smoke alarms
Tv remotes

33
Q

True or false, alkaline batteries are rechargeable

A

False

34
Q

Name for liquid that conducts electricity in the cell

A

Electrolyte

35
Q

How do chemical cells transfer energy to their surroundings

A

Electricity

36
Q

True or false, a battery has a higher voltage than a single cell

A

True

37
Q

Word used to describe lots of cells connected together and that increases voltage

A

Battery

38
Q

Electrochemical cells are called ‘electrochemical’ because they convert energy between what

A

Chemical and electrical forms

39
Q

Fuel cells convert the energy of what into electrical energy

A

Fuel and oxygen

40
Q

Most common type of fuel cell

A

Hydrogen - oxygen

41
Q

What is a common electrolyte used in hydrogen - oxygen fuel cells

A

Potassium hydroxide (KOH)

42
Q

Why are the anode and cathode in fuel cells different to in electrolysis

A

The positive and negative is the other way around
Cathode is positive
Anode is negative

43
Q

In fuel cells which out of the anode and cathode is positive

A

Cathode

44
Q

In fuel cells which out of the anode and cathode is negative

A

Anode

45
Q

In fuel cells what are both electrodes made from

A

(Porous) Carbon
There’s lots of tiny holes + a catalyst to speed up the reaction

46
Q

What is outside of the electrodes in fuel cells

A

A cathode compartment for the cathode
An anode compartment for the anode

47
Q

Where does hydrogen enter the fuel cell

A

Anode compartment

48
Q

Where does the oxygen enter the fuel cell

A

Cathode compartment

49
Q

In the fuel cell which side is the anode and which side is the cathode

A

Positive cathode is right
Negative anode is left

50
Q

Which compartment of the fuel cell does hydrogen enter

A

Negative anode on left

51
Q

Which compartment of the fuel cell does oxygen enter

A

Positive cathode on right

52
Q

Where do the heat and water leave once the reaction has taken place in the fuel cell

A

Outlet of cathode compartment

53
Q

In a fuel cell what do the hydrogen atoms do once they’ve entered the negative anode compartment on the left

A

Lose an electron to become a positive ion
(is oxidised as oxidation is loss of electrons)

54
Q

What happens in the fuel cell after the hydrogen atoms have each lost an electron at the positive anode on the left and turned into a positive ion (been oxidised)

A

Electrons and hydrogen ions move to cathode

The electron each hydrogen atom has lost passes through the wire to the positive cathode on the right
At the same time the hydrogen ions move through the electrolyte to the positive cathode on the right

55
Q

What happens once the positive hydrogen ions and electrons that they have lost reach the positive cathode on the right of the fuel cell

A

They react with the oxygen there to produce water

56
Q

What part of the reaction in the fuel cell is what generates the electricity

A

The electrons lost by the hydrogen atoms passing through the wire from the negative anode on left to positive cathode on right

57
Q

In fuel cells what is reduced and what is oxidised out of oxygen and hydrogen

A

Oxygen is reduced (gains electrons when it reacts to form water at the positive cathode on the right)
Hydrogen is oxidised (loses electrons at the negative anode on the left before it moves through the electrolyte to react with the oxygen in the cathode)

58
Q

In a hydrogen - oxygen fuel cell what is the fuel

A

Hydrogen

59
Q

One key use of hydrogen - fuel cells

A

Vehicles like cars
(Replaces fossil fuel engines)

60
Q

He is it good that hydrogen - fuel cells only require hydrogen and oxygen as the reactants

A

They are abundant
(There’s lots of hydrogen and oxygen)
They don’t produce any carbon dioxide/ other pollutants as waste

61
Q

True or false, fuel cells are relatively simple devices

A

True- they last longer than batteries and are less polluting to dispose of
This is an advantage of them

62
Q

Advantages of hydrogen - fuel cells

A

Only require hydrogen and oxygen which are in abundance
Less polluting than batteries to dispose of and last longer
Hydrogen and oxygen don’t produce any pollutants like CO2/ any waste

63
Q

Disadvantages of hydrogen - oxygen fuel cells

A

Because hydrogen is a gas it takes up much more space to store than fossil fuels/ batteries
Hydrogen is explosive when mixed with air so can be dangerous to store
The energy required to make hydrogen fuel usually comes from burning fossil fuels

64
Q

Disadvantages of hydrogen - oxygen fuel cells

A

Because hydrogen is a gas it takes up much more space to store than fossil fuels/ batteries
Hydrogen is explosive when mixed with air so can be dangerous to store
The energy required to make hydrogen fuel usually comes from burning fossil fuels

65
Q

What is the overall reaction for a hydrogen - oxygen fuel cell (word equation)

A

Hydrogen + oxygen -> water

66
Q

True or false, hydrogen and oxygen are both renewable

A

True

67
Q

True or false, hydrogen is dangerous to store

A

True
(Disadvantage of hydrogen - oxygen fuel cells)

68
Q

Describe how to calculate temperature change in an exothermic reaction (RPA) (in this case the reaction is the neutralisation of hydrochloric acid and sodium hydroxide)

A

Summary: Add increasing volumes of sodium hydroxide solution to the hydrochloric acid and for each different experiment (different volume of hydroxide) measure maximum temperature reached
IV- volume of sodium hydroxide
DV- maximum temperature reached
CV- volume of hydrochloric acid, concentration of acid and hydroxide solution

1) measure 30cm cubed of dilute hydrochloric acid in measuring cylinder
2) Transfer acid to cup inside beaker (stops cup from falling over)
3) use thermometer to measure temperature of acid
4) Use measuring cylinder to measure 5cm cubed or sodium hydroxide solution and add to the acid in the cup
5) place plastic lid over cup and place thermometer through hole in lid making sure it is in the solution
6) Gently stir solution with thermometer
7) look carefully at the temperature rise on the thermometer and record temperature when it stops rising (highest temperature reached)
8) Keep repeating the experiment, each time adding 5 more cm cubed of the hydroxide solution, stirring and then recording highest temperature reached
9) Stop once a maximum of 40cm cubed of hydroxide solution has been added to the acid
10) Repeat the whole experiment one more time to obtain 2 full sets of results and calculate mean value of maximum temperature reached for each volume of sodium hydroxide added
11) plot results on graph

69
Q

Explain the graph produced plotting results from seeing how volume of sodium hydroxide added to hydrochloric acid affects temperature change

A

As volume increases so does temperature change (because when more particles of sodium hydroxide are added they react with the acid and as it’s an exothermic reaction so thermal energy (heat) is given off (more reaction means more heat given off so maximum temperature increases)

However at certain volume of hydroxide, maximum temperature starts to decrease (there is so much hydroxide compared to acid that some of the hydroxide is unable to react and the maximum temperature reached by the reaction has already reached its maximum) Also as volume increases the temperature becomes more spread out

70
Q

Why should you use a lid when investigating temperature change (RPA)

A

To reduce heat loss through air which could make the maximum temperature reached appear lower than it should be

For cup use insulating material like polystyrene to prevent heat loss for sides and bottom

71
Q

Fuel cell half equation at negative electrode

A

H2 goes to 2H+ + 2e-

72
Q

Fuel cell half equation at positive electrode

A

O2 + 4H+ + 4e- goes to 2H2O

73
Q

Overall fuel cell equation

A

2H2 + O2 goes to 2H2O

74
Q

Describe overall process of fuel cell including half equations and overall equation

A

1) hydrogen enters inlet and is oxidised at negative electrode to form hydrogen ions
H2 goes to 2H+ + 2e-
2) lost electrons travel through wire to positive anode (generates electricity)
3) hydrogen ions travel through electrolyte to positive electrode and oxygen enters through inlet
4) hydrogen ions, electrons that have travelled round wire and oxygen all react to produce water
4H+ + 4e- + O2 goes to 2H2O

75
Q

2 Advantages of fuel cells over rechargeable cells and batteries (e.g for powering cars)

A

Rechargeable batteries eventually run out after a certain number of charges so need replacing (but fuel cells last for as long as they are supplied with fuel for

Rechargeable batteries have a smaller capacity so must be charged more frequently than fuel cells

GCSE Chemistry (18 decks)

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