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Science > Chemistry (C5) > Flashcards

Chemistry (C5) Flashcards

1
Q

Which type of reaction releases energy into the surroundings?

A

Exothermic

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2
Q

Which type of reaction absorbs energy from the surroundings?

A

Endothermic

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3
Q

In an exothermic reaction, what has more energy in it? The products or the reactants?

A

Reactants

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4
Q

In an endothermic reaction, what has more energy in it? The products or the reactants?

A

Products

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5
Q

What would happen to the temperature of the surroundings in an exothermic reaction?

A

Increase

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6
Q

What would happen to the temperature of the surroundings in an endothermic reaction?

A

Decrease

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7
Q

Give three examples of endothermic reactions.

A

Thermal decomposition reactions
Citric acid + sodium hydrogen carbonate
Sports injury packs
Photosynthesis

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8
Q

Give three examples of exothermic reactions.

A

Combustion
Oxidation
Neutralisation
Displacement
Respiration
Self-heating cans
Hand warmers

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9
Q

What is the unit for temperature?

A

Degrees Celsius (oC)

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10
Q

Describe how to determine the temperature change of the reaction between hydrochloric acid and sodium hydroxide solutions.

A

• Put a measured volume of hydrochloric acid and pour into a polystyrene cup with a lid.
• Record the initial temperature using a thermometer.
• Add a measured volume of sodium hydroxide into the beaker and stir, replace lid.
• Record the final temperature of the mixture.
• Calculate the temperature change of the reaction.

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11
Q

Define ‘activation energy’.

A

Minimum amount of energy that particles must collide with to react.

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12
Q

What is the substance called that reduces the activation energy required by a reaction?

A

Catalyst

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13
Q

Is energy released when bonds are broken or bonds are made?

A

Made

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14
Q

Is energy absorbed when bonds are broken or bonds are made?

A

Broken

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15
Q

Describe an endothermic reaction in terms of bond making and breaking.

A

More energy is required to break the bonds than is released when bonds are made.

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16
Q

Describe an exothermic reaction in terms of bond making and breaking.

A

More energy is released when bonds are made than is required to break the bonds.

17
Q

State how to calculate energy change in a reaction.

A

Overall energy change = sum of energy required to break bonds – sum of energy released making bonds.

18
Q

What type of energy change would an exothermic reaction have?

A

Negative (energy is released)

19
Q

What type of energy change would an endothermic reaction have?

A

Positive (energy is taken in)

20
Q

What is an electrolyte?

A

A liquid that conducts electricity.

21
Q

Explain why sodium chloride solution is a good electrolyte.

A

It contains positive and negative ions that are free to move and carry their charge.

22
Q

Describe how to make a simple chemical cell.

A

Connect two pieces of different metals (electrodes) to an electrolyte.

23
Q

Describe how to make a chemical battery.

A

Connect two or more chemical cells together in series.

24
Q

What two factors affect the potential difference (voltage) produced by a chemical cell/battery?

A
  1. The metals used as electrodes
  2. The electrolyte used
25
Q

Which two metals used in a chemical cell would produce the biggest voltage? Why?

A

Aluminium and copper

The bigger the difference in reactivity, the bigger the voltage produced.

26
Q

What is the chemical difference between a rechargeable and non-rechargeable cell?

A

Renewable cells - chemical reaction reversed by an external electrical current.

27
Q

Non-rechargeable cells/batteries work until…

A

One of the reactants is used up.

28
Q

Which type of reaction occurs in a rechargeable cell?

A

Reversible.

29
Q

Which type of battery is more expensive initially? Rechargeable or non-rechargeable?

A

Rechargeable.

30
Q

Which type of battery is more expensive in the long term?

A

Non-rechargeable.

31
Q

What is the name of the fuel cell in which hydrogen is oxidised to produce water and energy?

A

Hydrogen fuel cell.

32
Q

What is the word equation for the reaction taking place in a hydrogen fuel cell?

A

Hydrogen + oxygen → water.

33
Q

Suggest two advantages of using hydrogen fuel cells over rechargeable batteries.

A

• The only waste product of hydrogen fuel cells is water.
• Keep producing electricity as long as fuel is provided.

34
Q

Suggest two disadvantages of using hydrogen fuel cells over rechargeable batteries.

A

• They are very expensive.
• Difficult to transport and store hydrogen as it is a flammable gas.
• Most hydrogen comes from methane in natural gas (fossil fuel).

35
Q

What is the half equation for the reaction at the cathode in a hydrogen fuel cell? Is this oxidation or reduction?

A

O2 + 4H+ + 4e- → 2H2O

Reduction.

36
Q

What is the half equation for the reaction of hydrogen at the anode in a hydrogen fuel cell? Is this oxidation or reduction?

A

2H2 → 4H+ + 4e-

Oxidation.

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