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Chemistry Year 10 (GCSE) AQA > C5- Energy Changes > Flashcards

C5- Energy Changes Flashcards

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1
Q

What is an exothermic reaction?

A

A reaction where energy is transferred to the surroundings.

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2
Q

Give examples of exothermic reactions.

A

1) Combustion
2) Respiration
3) Neutralisation reactions.

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3
Q

What happens to the temperature of the surroundings during an exothermic reaction?

A

The temperature of the surroundings increases.

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4
Q

What is an endothermic reaction?

A

A reaction where energy is transferred from the surroundings.

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5
Q

Give examples of endothermic reactions.

A

1) Thermal decomposition reactions.
2) The reaction between citric acid and sodium hydrogen carbonate.
3) Certain respiration.

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6
Q

What happens to the temperature of the surroundings during an endothermic reactions?

A

The temperature of the surroundings decrease.

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7
Q

State two uses of exothermic reactions.

A

1) Self-heating cans.

2) Hand warmers.

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8
Q

State a use of endothermic reactions.

A

Some cooling sports injury packs.

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9
Q

What are reactants?

A

The substances involved in a chemical reaction.

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10
Q

What are products?

A

The substances formed when reactants have a chemical reaction.

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11
Q

What is a reaction profile?

A

A diagram which shows whether the reactants have more or less energy than the products.

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12
Q

Why does the reaction profile always go up at the start?

A

A reaction starts with bonds being broken.

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13
Q

What is the activation energy.?

A

The energy needed to break bonds to start a reaction.

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14
Q

Why does the reaction profile always go down at the end?

A

A reaction always ends with bonds being made.

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15
Q

If the reactants have more energy than the products, what kind of a reaction must have taken place?

A

An exothermic one. Energy has been transferred to the surroundings.

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16
Q

If the reactants have less energy than the products, what kind of a reaction must have taken place?

A

An endothermic one. Energy has been taken in from the surroundings.

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17
Q

Is breaking bonds endothermic or exothermic?

A

Endothermic. Chemical bonds are strong so require energy to break (like when you have to put energy in to separate magnets from each other).

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18
Q

Is making bonda endothermic or exothermic?

A

Exothermic. Energy is released when chemical bonds are formed (like how two magnets move together when close and generate kinetic energy).

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19
Q

How do we work out the overall energy change of a reaction?

A

Work out the difference between the energy needed to break all the bonds in the reactants and the energy released to form all the bonds in the products.

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20
Q

How do we work out the energy change from a reaction profile?

A

The difference between the energy of the reactants and the energy of the products.

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21
Q

How do we work out the activation energy from a reaction profile?

A

The difference between the energy of the reactants and the highest point on the profile.

22
Q

What is a chemical cell?

A

A unit which contains chemicals which produce electricity through a reaction.

23
Q

What are the main components of a chemical cell?

A

An anode, a cathode (made of 2 different metals and an electrolyte.

24
Q

What is an electrolyte?

A

A solution containing ions.

25
Q

What does the voltage of a cell depend on?

A

The type of electrode and the electrolyte.

26
Q

What is a battery?

A

Two or more cells connected in series.

27
Q

What happens to the electrodes in a chemical cell?

A

The more reactive metal is used up and the less reactive on increases in size.

28
Q

In non-rechargeable cells, why do the chemical reactions stop over time?

A

One of the reactants become used up.

29
Q

How can certain cells be recharged?

A

Applying an external electric current.

30
Q

How does the reactivity of the metal electrodes affect the size of the potential difference?

A

Which way do electrons move in a cell?

31
Q

What is a fuel cell?

A

A cell which uses a fuel and oxygen (or air) to generate electricity.

32
Q

What are the products in a hydrogen fuel cell?

A

Water.

33
Q

State 2 advantage of hydrogen fuel cells.

A

1) Do not need to be recharged.

2) No pollutants are produced.

34
Q

State three disadvantages of hydrogen fuel cells.

A

1) Hydrogen is highly flammable.
2) Hydrogen is often made from fossil fuels.
3) Hydrogen is difficult to store.

35
Q

What reaction occurs at the positive electrode of a hydrogen fuel cell?

A

O2 + 4Hᐩ + 4e⁻ -> 2H₂O

36
Q

Which reaction occurs at the negative electrode of a hydrogen fuel cell?

A

H₂ -> 2H + 2e⁻

37
Q

Give 2 examples of fuels.

A

1) Natural gas

2) Methane

38
Q

How do sports injury packs work?

A

When squeezed forcefully, ammonium nitrate and water mix in the pack, resulting in instant cooling.

39
Q

Give the 2 requirements for a successful reaction to take place.

A

1) Collision= Particles of the reactants have to collide.
2) Activation energy= The collisions that happen between particles of the reactants must take place with enough energy. This threshold amount of energy is called the activation energy.

40
Q

How do catalysts work in reactions?

A

They increase the rates of reactions by decreasing the activation energy, which increases the chance of successful collisions.

41
Q

How can we figure out whether a reaction is endothermic or exothermic?

A

By subtracting the total bond energies of the products from the total bond energies of reactants, we can see if a reaction is endothermic or exothermic.

42
Q

Give the rule for the energies of bonds in exothermic reactions.

A

Energy released by making bonds > energy required to break bonds.
I.e. overall energy change of reaction < 0

Endothermic reactions

43
Q

Give the rule for the energies of bonds for endothermic reactions.

A

Energy released by making bonds < energy required to break bonds.
I.e. overall energy change of reaction > 0

44
Q

Define a battery

A

A battery is a collection of more than one cell joined in series (end-to-end).

45
Q

How do you calculate the voltage of a battery?

A

It is the sum of the voltages of the individual cell components.

46
Q

Give 4 advantages to fuel cells.

A

1) Reliable
2) Less pollution than traditional methods
3) High efficiency
4) Compact and lightweight.

47
Q

How do fuel cells produce electricity?

A

Fuel cells produce electrical energy efficiently by using energy produced by a particular reaction.

48
Q

What is the reaction used in fuel cells to produce electrical energy?

A

The reaction is between an external fuel source and oxygen. Once added to the cell, the fuel is oxidised, this causes a voltage to be established.

49
Q

What is the only waste product of a hydrogen fuel cell?

A

Water

50
Q

What is the half equation for the negative electrode in a hydrogen fuel cell?

A

2H₂ -> 4H⁺ + 4e⁻

51
Q

What is the half equation for the positive electrode of a hydrogen fuel cell and what happens here?

A

O₂ + 4H⁺ + 4e⁻ -> 2H₂O

Oxygen combines with the hydrogen to form this product. (Water) The hydrogen is being oxidised.

52
Q

What is the overall equation for a hydrogen fuel cell?

A

2H₂ + O₂ -> 2H₂O

Chemistry Year 10 (GCSE) AQA (5 decks)

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