Topic 5 - Chemical Reactions Flashcards Preview

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Flashcards in Topic 5 - Chemical Reactions Deck (25)
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1
Q

Describe the endothermic reaction of sodium chloride into sodium and chlorine.

A

NaCl –> Na + Cl

-Originally strong bonds between the sodium and chlorine, and energy is supplied to break the bonds.

2
Q

What happens during a chemical reaction?

A

Old bonds are broken and new ones form.

3
Q

Describe the exothermic reaction of magnesium and oxygen into magnesium oxide.

A

Mg+O—->MgO+energy released

-The magnesium and oxygen form a strong bond

4
Q

What is meant by the term ‘exothermic reaction’?

A

An exothermic reaction is one which overall gives out energy to the surroundings in the form of heat, shown by a rise in temperature.

5
Q

Give some examples of exothermic reactions.

A

Combustion (water and carbon dioxide form requiring energy)

Explosions

6
Q

What is meant by the term ‘endothermic reaction’?

A

An endothermic reaction is one which overall takes in energy from the surroundings in the form of heat, shown by a fall in temperature.

7
Q

Give some examples of an endothermic reaction.

A
  • Photosynthesis (light energy from sun to convert carbon dioxide and water into glucose and oxygen)
  • Ammonium nitrate (dissolves in water it takes in heat from surroundings)
8
Q

Which are more common, endothermic or exothermic reactions?

A

Exothermic

9
Q

Describe the energy levels throughout an exothermic reaction

A
  • Reactants are at a higher energy than the products. -Difference in height represents energy given out in the reaction.
  • The initial rise represents the activation energy - energy needed to break old bonds.
10
Q

Describe the energy levels throughout an endothermic reaction.

A
  • Reactants are at a lower energy than the products.

- The difference in height represents energy taken in during a reaction.

11
Q

What are the four reactions where you could measure a change in temperature?

A
  • Dissolving salts in water.
  • Neutralisation reactions (acid & base reacting together).
  • Displacement reactions (more reactive element taking the place of a less reactive element)
  • Precipitation reactions (two solutions react to form an insoluble precipitate)
12
Q

Give an example of:
A) a slow reaction.
B) a moderate reaction.
C) a (very) fast reaction

A

A) rusting of iron
B) metal reacting with acid forming a gentle steam of bubbles
C) explosion

13
Q

What are the four factors that influence rate of reaction?

A

Temperature
Concentration/pressure (gas)
Catalyst
Surface area (solid)/size of particles

14
Q

Explain the reaction of hydrochloric acid with marble chips

A
  • Used to show effect of increasing surface area of a solid.
  • Measure volume of gas evolved with a gas syringe at regular intervals.
  • Repeat with same volume of acid and mass of marble chips, just more crushed up (to increase surface area), including repeat with powdered marble.
  • Experiment can also show how concentration of acid affects the rate of reaction. -Change concentration of hydrochloric acid each time and keep other factors the same.
  • Can also find the rate of reaction by measuring total mass of the flake during the reaction.
15
Q

Explain the reaction of sodium thiosulfate and hydrochloric acid

A
  • Both chemicals are clear solutions, and react together to form a yellow precipitate of sulphur.
  • Tim how long it takes a black mark to disappear as the solution forms the cloudy sulphur.
  • Repeat reaction for different temperatures (water bath to heat solutions to the right temperature before mixing).
  • Must keep the depth of the liquid the same for each.
  • Results will show the higher the higher the temperature, the quicker the reaction and therefore takes less time for the black mark to disappear.
  • Negative: can not get graphs, just a set of readings.
16
Q

What is meant by the term ‘catalyst’?

A

A catalyst is a substance which changes the speed of a reaction, without being used up in the reaction.

17
Q

Explain how a catalyst works.

A
  • Lowers the activation energy.
  • Makes it easier for the reaction to happen & increases the rate of the reaction.
  • Means a lower temperature can be used, without lowering the rate of reaction.
18
Q

Where is a catalytic converter found?

A

In the exhaust pipe of motor vehicles

19
Q

Explain how a catalytic converter works in vehicles.

A
  • Vehicles can give off poisonous gases like carbon monoxide when petrol doesn’t burn properly.
  • Catalytic converters increase the rate carbon monoxide & unburnt fuel in exhaust gases react with oxygen in the air to produce carbon dioxide and water.
  • Has a large surface area & works best at high temperatures to increase the rate of reaction.
20
Q

What are the four things that affect the rate of chemical reactions?

A
  • Temperature - higher temperature increases the rate of reaction & vice versa.
  • Concentration/pressure - higher concentration/pressure increases the rate of reaction & vice versa.
  • Surface area - larger surface area increases the rate of reaction & vice versa.
  • Use of a catalyst - using a catalyst increases the rate of reaction.
21
Q

Explain how a higher temperature increases collisions and therefore rate of reaction.

A

When temperature increases, the particles move quicker.

If they move faster, they have more frequent collisions.

22
Q

Explain how a higher concentration/pressure increases the rate of reaction

A
  • More particles of the reactant colliding with other molecules.
  • Makes collisions between particles more likely.
  • In a gas, increasing the pressure means that particles are more squashed up together so there are more frequent collisions.
23
Q

Explain how a larger surface area increases the rate of reaction.

A
  • Has a larger surface area by being broken down into smaller pieces.
  • Particles around it in the solution will have a larger surface area to react with, so there will be more frequent collisions.
24
Q

Explain how a catalyst increases the rate of a reaction.

A

Gives the particles reacting a surface to stick to.

Increases the number of successful collisions by lowering the activation energy.

25
Q

What ONE way can you get faster collision?

A

Faster collisions are ONLY caused by an increase in temperature.