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Chemistry > Rates of Reactions > Flashcards

Rates of Reactions Flashcards

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1
Q

What is reaction rate?

A

How fast a reaction happens

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2
Q

How is reaction rate observed?

A

Measuring how quickly reactants are turned into products or how quickly they are used up

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3
Q

Formula for rate of reaction

A

Amount of reactant used or amount of product formed / time

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4
Q

Benefits of fast reactions in industry

A

Making the required product as cheaply as possible maximises profit
Yield more product in a given time

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5
Q

Drawbacks of fast reactions in industry

A

Expensive to generate conditions

Safety concerns

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6
Q

What does the collision theory explain?

A

Why reactions occur at different rates and how they occur

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7
Q

What does the collision theory state must happen for chemical reactions to occur?

A

Particles must collide with enough energy (the activation energy)

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8
Q

What does the rate of a chemical reaction depend on?

A

Frequency of collisions between reacting particles

Amount of energy transferred in a collision

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9
Q

What does increasing the rate of reaction mean increasing?

A

The number of collisions and / or energy of reacting particles

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10
Q

How can we increase the rate of reaction?

A

Increase temperature
Increase concentration/ pressure in gases
Increase surface area to volume ratio

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11
Q

How can we calculate reaction rates from a graph?

A

Draw tangent and work out it’s gradient

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12
Q

What does a smaller gradient tell us?

A

Slower rate of reaction

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13
Q

How can we observe how concentration affects reaction rate? What is seen?

A

Precipitation reaction

A colour change

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14
Q

What solutions must we use for a precipitation reaction?

A

2 see through solutions that mix to form a precipitate which clouds the solution

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15
Q

What are 2 solutions we could use in a precipitation reaction?

A

Sodium thiosulfate and hydrochloric acid

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16
Q

How is a precipitation reaction carried out?

A

Put a conical flask on top of a sheet of paper with an X in the centre
Pour in solution that is not acid
Pour in acid with a known concentration and press start on stop watch
Stop when you can’t see X

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17
Q

What should we repeat precipitation reactions with?

A

Different acid concentrations

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18
Q

What are the independent and dependent variables for precipitation reactions?

A

Acid concentration

Time taken for cross to disappear

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19
Q

How can reaction rate be measured with a mass change?

A

A gas is released and lost mass is measured on a mass balance

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20
Q

What shows a faster reaction in a mass change experiment?

A

Quicker the reading on the mass balance drops

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21
Q

How do we show surface area affecting reaction rate?

A

Hydrochloric acid and marble chips

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22
Q

Experiment to show surface area affecting reaction rate

A

Place a known mass of marble chips in a measuring cylinder and pour in an excess volume of acid with a known concentration
Record volume of gas given off every second using a gas syringe

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23
Q

What are the independent and dependent variables in the surface area experiment?

A

Surface area of the marble chips

Volume of gas given off each second

24
Q

When had the marble chip reaction finished?

A

When no more gas is produced

25
Q

How should the surface area experiment be repeated?

A

Same volume and concentration of acid and the same mass of marble chips but with more crunched up (increased surface area)
Then repeat with powdered chalk

26
Q

What chemicals are used to measure how temperature affects reaction rate?

A

Sodium thiosulfate

Hydrochloric acid

27
Q

What do sodium thiosulfate and hydrochloric acid react to form?

A

Yellow precipitate of sulfur

28
Q

In the experiment to measure how temperature affects reaction rate, what is the measure of this reaction?

A

The time taken for the precipitate to form

29
Q

Steps for temperature experiment

A

Measure out fixed volumes of sodium thiosulfate and hydrochloric acid using a measuring cylinder and heat in a water bath to a desired temperature
Mix in a conical flask and place on white paper with a cross on it
Time how long it takes for black cross to disappear

30
Q

How should the experiment to measure temperature affecting reaction rate be changed?

A

Different temperatures

31
Q

Why does increasing temperature increase reaction rate?

A

Increases collision frequency

Makes reactants gain energy so a greater proportion will have more energy than activation energy needed

32
Q

Why does increasing concentration/ pressure increase rate of reactions?

A

Higher collision frequency

More particles of the same reactant in the same volume

33
Q

What do catalysts do?

A

Increase reaction rates

34
Q

Why are catalysts used in industrial reactions?

A

Reduce energy costs

35
Q

Why are catalysts efficient?

A

Aren’t chemically changed or used up in reactions

Small amount needed to catalyse large amounts of reactants

36
Q

What will catalysts not change?

A

Products

37
Q

Why do catalysts increase the likelihood of collisions?

A

Decrease activation energy needed for a reaction to occur

38
Q

How do catalysts decrease activation energy?

A

Provide an alternative reaction pathway that has a lower activation energy

39
Q

What show a reaction’s progress?

A

Reaction profiles

40
Q

What happen during chemical reactions?

A

Energy changes

41
Q

What does an increase / decrease in temperature depend on?

A

Which reagents are used in the reaction

42
Q

What reactions cause changes in heat energy?

A

Salts dissolving in water
Neutralisation - most exothermic
Displacement - most exothermic
Precipitation - exothermic

43
Q

Experiment to measure temperature change when dissolving salts in water

A

Add salt to polystyrene cup of water and measure temperature change when salt has dissolved

44
Q

Exothermic reactions

A

Energy from reacting chemicals transferred to surroundings leading to temperature increase

45
Q

Examples of exothermic reactions

A

Combustion
Neutralisation
Oxidation
Hand warmers

46
Q

Endothermic reactions

A

Energy from surroundings transferred to reacting chemicals, decreasing temperature of the surroundings

47
Q

Examples of endothermic reactions

A

Sports injury packs
Thermal decomposition
Citric acid + baking soda

48
Q

What must be supplied to break bonds? What type of reaction is this?

A

Energy

Endothermic

49
Q

What happens to bonds during a chemical reaction?

A

Old bonds are broken and new bonds are formed

50
Q

What is released when new bonds are formed? What type of reaction is this?

A

Energy

Exothermic

51
Q

Bond energy calculations

A

Overall energy = energy required to break bonds - energy released by forming bonds

52
Q

What is overall energy change measured in?

A

KJ mol-1

53
Q

Experiment to measure change in temperature of a reaction

A

Polystyrene cup into large beaker of cotton wood
Add known volume of reagent to cup and measure initial temperature of the solution
Add measured mass of second reagent and stir
Put a lid on cup
Record max/ min temperature that it reaches
Calculate temperature change

54
Q

Why is a polystyrene cup used? What does it reduce?

A

Good thermal insulator

How much the external temperature affects the reaction

55
Q

Why is cotton wool used? What does it reduce?

A

Gives insulation

Energy transfer to or from reaction mixture

Chemistry (5 decks)

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