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

Controlling the Rate Flashcards

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
What is temperature a measure of?
the average kinetic energy of particles in a substance
26
What are energy distribution diagrams also called and what are they used to show?
Called Boltzmann distribution | Used to show the distribution of kinetic energy that particles have in a substance.
27
What is activation energy?
the minimum kinetic energy required by colliding particles before a reaction may occur.
28
What does increasing the temperature of a reaction do?(4)
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
How can the change of rate during a reaction be monitored ?
By understanding the different stages of a graph
30
Describe stage 1 of graph ?(3)
Reaction is rapid High concentration of reactants Many successful collisions
31
Describe stage 2 of graph ?
Reaction slowing down as reactants being used up Concentration of reactants is decreasing Less successful collisions
32
Describe stage 3 of graph?
Reaction effectively at end At least one of the reactants has been used up No more collisions
33
What can a catalyst do?
Increase the rate of a chemical reaction
34
What is special about catalyst ?
They increase the rate of a reaction without being used up
35
What do catalysts allow the reaction to occur at?
A lower temperature
36
What do catalyst do to increase the rate of a reaction?
They decrease the activation energy
37
What does using a catalyst provide?
An alternative reaction pathway with a lower activation energy
38
What does using a catalyst cause ?
More particles to have energy equal or greater than the activation energy value
39
What does using a catalyst result in?
More successful collisions
40
What does using a catalyst do?
Increase the rate of a reactions
41
What can potential energy diagrams be used to show?
The energy pathway for a reaction.
42
What do potential energy diagrams indicate ?
If a reaction is exothermic or endothermic
43
What is an exothermic reaction?
A reaction where energy is given out to surroundings and the energy change is from chemical➡️heat
44
How can you identify an exothermic reaction?
Temperature of surroundings increase
45
What is an endothermic reaction ?
A reaction where energy is absorbed from the surroundings and the energy change is from heat➡️chemical
46
How can you identify an endothermic reaction?
Temperature of surroundings decrease
47
What happens during a reaction(in terms of bonds)?(2)
Bonds are broken | New bonds form
48
What bonds are broken, the reactants or the products ?
Reactants
49
What are the new bonds formed, the reactants or the products?
Products
50
What is required to break bonds and what is the reaction said to be then?
Energy is required therefore the reaction is said to be endothermic
51
What is released when new bonds are made and what is the reaction said to be then?
Energy is released therefore the reaction is said to be exothermic
52
What is the enthalpy change ?
The difference in energy between the products and reactants
53
What is the equation for enthalpy change?
/\H=energy of products-energy of reactants
54
Describe the appearance of a potential energy diagram for an exothermic reaction?
Reactants higher than the products because the reactants have more chemical energy
55
What are enthalpy changes in exothermic reactions always?
Negative
56
What units do you use when calculating the enthalpy change?
kJ mol-1
57
Describe the appearance of the potential diagram for a endothermic reaction ?
Products higher than the reactants because they have more chemical energy than the reactants
58
What are enthalpy changes in endothermic reactions always?
Positive
59
What can the activation energy also be described as?
The minimum energy required by colliding particles to form an activated complex
60
Where is the activated complex on the potential energy diagram ?
Maximum point
61
What is the activated complex?
It is the energy that reactant particles must overcome in order to form the product
62
What are the 2 types of reaction in terms of potential energy diagrams?
Forward reaction r➡️p | Reverse reaction p➡️r
63
What is meant by activated complex?
as unstable arrangement of atoms formed as reactant bonds are broken and product bonds are formed.
64
What will the activation energy for forward and reverse reactions always be?
different
65
What will enthalpy change for forward and reverse reactions remain?
constant apart from the sign (+/-)
66
What does the rate of reaction not depend on?
enthalpy change
67
What does a catalyst not alter?
the enthalpy change of the reaction

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

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