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Higher Chemistry Unit 1: Chemical changes and structure > Controlling the Rate > Flashcards

Controlling the Rate Flashcards

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1
Q

What are the 3 ways reactions can be followed?

A

By measuring changes in concentration, mass and volume of reactants and products.

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2
Q

When measuring the decrease in mass (e.g. of flask), what apparatus do you use?

A

conical flask (containing contents e.g. HCl + marble chips)
balance
cotton wool

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3
Q

What is cotton wool used to do when measuring the decrease in mass?

A

prevent spray

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4
Q

When measuring the decrease in mass (of flask) what should the graph look like?

A

graph slopes downwards

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5
Q

When measuring the decrease in concentration (of acid) what should the graph look like?

A

graph slopes downwards

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6
Q

What are the 2 ways of measuring the volume of gas produced?

A

using a gas syringe

using an inverted measuring cylinder

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7
Q

When measuring the volume of gas produced, what apparatus is used specifically when using a gas syringe?

A

conical flask(with contents e.g. HCl + marble chips)
stopper
delivery tube
gas syringe

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8
Q

When measuring the volume of gas produced, what apparatus is used specifically when using an inverted measuring cylinder?

A 
conical flask(with contents e.g. HCl + marble chips)
stopper
delivery tube
water basin e.g. ice cream tub
inverted measuring cylinder
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9
Q

When measuring the volume of gas produced, what does the graph look like?

A

graph slopes upwards

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10
Q

What is the equation used to find the average rate of a reaction?

A

Average rate= change in variable / change in time

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11
Q

What do the units of average rate depend on?

A

the variable used. e.g. concentration mol l-1 s-1
mass g s-1
volume cm3 s-1

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12
Q

For some reactions what will a colour change indicate?

A

the end of the reaction e.g. from colourless to blue/black

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13
Q

During a reaction where there is a colour change, what is the only measurement can be recorded?

A

time

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14
Q

As there is no change in variable, what is equation do we use to express the rate?

A

relative rate= 1/time

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15
Q

What unit is used for relative rate?

A

s-1

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16
Q

What equation do we use when we are given the relative rate and need to calculate the time?

A

time=1/relative rate

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17
Q

What does the collision theory state must happen for a reaction to take place?(2)

A

reacting particles must successfully collide with one another.
the collision must have enough energy

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18
Q

What 5 factors can alter the number of successful collisions during a chemical reaction and thus increase the reaction rate?

A 
concentration
pressure 
particle size/surface area
collision geometry 
temperature
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19
Q

What does increasing the concentration of a solution do?(3)

A

increases the number of particles in a given volume.
more particles will result in a greater chance of successful collisions.
therefore increase the reaction rate.

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20
Q

What does increasing the pressure of a reaction do?(3)

A

increases the number of particles in a given volume.
more particles will result in a greater chance of successful collisions.
therefore increase the reaction rate.

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21
Q

Where can the reactions of solids only take place at?

A

at the surface of the solid

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22
Q

What do smaller particles have?

A

a larger surface area

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23
Q

What does a larger surface area result in?(2)

A

a greater number of successful collisions

therefore increases the reaction rate

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24
Q

If reactant particles do not strike each other at the correct orientation (angle), what will happen?

A

a product will not form as the collisions will have been unsuccessful.

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25
Q

What is temperature a measure of?

A

the average kinetic energy of particles in a substance

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26
Q

What are energy distribution diagrams also called and what are they used to show?

A

Called Boltzmann distribution

Used to show the distribution of kinetic energy that particles have in a substance.

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27
Q

What is activation energy?

A

the minimum kinetic energy required by colliding particles before a reaction may occur.

28
Q

What does increasing the temperature of a reaction do?(4)

A

Gives the particles more energy
This causes an increase in the number of particles with energy greater than or equal to the activation energy
This will result in a greater chance of successful collisions
Therefore increase the reaction rate

29
Q

How can the change of rate during a reaction be monitored ?

A

By understanding the different stages of a graph

30
Q

Describe stage 1 of graph ?(3)

A

Reaction is rapid
High concentration of reactants
Many successful collisions

31
Q

Describe stage 2 of graph ?

A

Reaction slowing down as reactants being used up
Concentration of reactants is decreasing
Less successful collisions

32
Q

Describe stage 3 of graph?

A

Reaction effectively at end
At least one of the reactants has been used up
No more collisions

33
Q

What can a catalyst do?

A

Increase the rate of a chemical reaction

34
Q

What is special about catalyst ?

A

They increase the rate of a reaction without being used up

35
Q

What do catalysts allow the reaction to occur at?

A

A lower temperature

36
Q

What do catalyst do to increase the rate of a reaction?

A

They decrease the activation energy

37
Q

What does using a catalyst provide?

A

An alternative reaction pathway with a lower activation energy

38
Q

What does using a catalyst cause ?

A

More particles to have energy equal or greater than the activation energy value

39
Q

What does using a catalyst result in?

A

More successful collisions

40
Q

What does using a catalyst do?

A

Increase the rate of a reactions

41
Q

What can potential energy diagrams be used to show?

A

The energy pathway for a reaction.

42
Q

What do potential energy diagrams indicate ?

A

If a reaction is exothermic or endothermic

43
Q

What is an exothermic reaction?

A

A reaction where energy is given out to surroundings and the energy change is from chemical➡️heat

44
Q

How can you identify an exothermic reaction?

A

Temperature of surroundings increase

45
Q

What is an endothermic reaction ?

A

A reaction where energy is absorbed from the surroundings and the energy change is from heat➡️chemical

46
Q

How can you identify an endothermic reaction?

A

Temperature of surroundings decrease

47
Q

What happens during a reaction(in terms of bonds)?(2)

A

Bonds are broken

New bonds form

48
Q

What bonds are broken, the reactants or the products ?

A

Reactants

49
Q

What are the new bonds formed, the reactants or the products?

A

Products

50
Q

What is required to break bonds and what is the reaction said to be then?

A

Energy is required therefore the reaction is said to be endothermic

51
Q

What is released when new bonds are made and what is the reaction said to be then?

A

Energy is released therefore the reaction is said to be exothermic

52
Q

What is the enthalpy change ?

A

The difference in energy between the products and reactants

53
Q

What is the equation for enthalpy change?

A

/\H=energy of products-energy of reactants

54
Q

Describe the appearance of a potential energy diagram for an exothermic reaction?

A

Reactants higher than the products because the reactants have more chemical energy

55
Q

What are enthalpy changes in exothermic reactions always?

A

Negative

56
Q

What units do you use when calculating the enthalpy change?

A

kJ mol-1

57
Q

Describe the appearance of the potential diagram for a endothermic reaction ?

A

Products higher than the reactants because they have more chemical energy than the reactants

58
Q

What are enthalpy changes in endothermic reactions always?

A

Positive

59
Q

What can the activation energy also be described as?

A

The minimum energy required by colliding particles to form an activated complex

60
Q

Where is the activated complex on the potential energy diagram ?

A

Maximum point

61
Q

What is the activated complex?

A

It is the energy that reactant particles must overcome in order to form the product

62
Q

What are the 2 types of reaction in terms of potential energy diagrams?

A

Forward reaction r➡️p

Reverse reaction p➡️r

63
Q

What is meant by activated complex?

A

as unstable arrangement of atoms formed as reactant bonds are broken and product bonds are formed.

64
Q

What will the activation energy for forward and reverse reactions always be?

A

different

65
Q

What will enthalpy change for forward and reverse reactions remain?

A

constant apart from the sign (+/-)

66
Q

What does the rate of reaction not depend on?

A

enthalpy change

67
Q

What does a catalyst not alter?

A

the enthalpy change of the reaction

Higher Chemistry Unit 1: Chemical changes and structure (3 decks)

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