Chemistry Rate Of Reaction Unit

Question 1

What must happen for a reaction to be successful?

COLLISION THEORY

Answer 1

-For a reaction to be successful reactant particles MUST collide with the correct orientation and have energy greater than the activation energy

Question 2

What must happen to speed up a reaction?

Answer 2

-To speed up a chemical reaction you must increase the frequency of successful collisions

Question 3

Define activation energy.

Answer 3

-Activation energy is the minimum amount of energy required for a reaction to take place and successful collisions to occur

Question 4

What happens when activation energy is higher?

Answer 4

-If it is higher, fewer collisions will have the energy required so the reaction will occur more slowly

Question 5

Define reaction rate.

Answer 5

-Reaction rate is defined as the amount of reactant used up or the amount of product produced in a given amount of time

Question 6

What are the four conditions that affect the rate of reaction?

Answer 6

-Presence of a catalyst
-Surface area
-Temperature
-Concentration

Question 7

Why do scientist need to understand rates of reaction?

Answer 7

-Safety (how much gas or heat might be released in a short space of time)
-Medicines (how much is required for a therapeutic effect to avoid negative effects)
-Profit per unit of time (when making a substance for sale)

Question 8

Define catalyst.

Answer 8

A catalyst is a substance which speeds up a chemical reaction by lowering the activation energy, remaining unchanged by the reaction

Question 9

How does surface area affect rate of reaction?

Answer 9

-If we increase the surface area of a solid reactant, more reactant particles are exposed to each other, leading to an increase of the frequency of collisions (and hence the frequency of successful collisions
-This means that an increase in surface area results in a higher reaction rate

Question 10

How does temperature affect the rate of reaction?

Answer 10

If we increase the temperature:
1. The reactant particles will have more kinetic energy, and so
2. More particles will have sufficient energy to form products, and
3. Therefore the frequency of successful collisions (and hence reaction rate) increases

Question 11

What is the unit for concentration?

Answer 11

molL^-1

Question 12

How does concentration affect the rate of reaction?

Answer 12

Increasing the concentration means:
1. There are more reactant particles in a given volume of space, so
2. particles collide more frequently, so
3. successful collisions happen more frequently, increasing reaction rate

Question 13

How do we measure rate of reaction?

Answer 13

1. Measure the volume of gas produced over time
2. Measure how long it takes for a colour change to occur (opaque)
3. Time how long it takes for a reactant to react away (disappear)
4. Record the mass lost form a reaction over time

All of these methods involve time as a crucial aspect.

Question 14

Define exothermic reaction.

Answer 14

Exothermic reactions are reactions that give out heat (release) heat energy to the surroundings.

Question 15

Define endothermic reaction.

Answer 15

Endothermic reactions are reactions that take in (absorb) energy from the surroundings
-Energy is transferred as heat energy from the surroundings into the reaction

Question 16

How do you calculate the activation energy?

Answer 16

Peak-reactants

Question 17

How do you start any reaction?

Answer 17

You must break the bonds of the reactants

Question 18

What does the arrow between the reactants and the products mean?

Answer 18

The loss or gaining of chemical energy in the reaction

Question 19

How do you calculate the overall energy change?

Answer 19

Products-reactants (doesn’t matter if the answer is negative)
-Exothermic will be negative
-Endothermic with be positive

Question 20

Do catalysts change the overall energy change?

Answer 20

No, the difference between the reactants and products remains the same, only the activation energy, which has decreased, is different

Question 21

What does the S.A.M.E acronym stand for?

Answer 21

Subjectivity: Did the practical involve any aspect which was down to human judgement?
Amounts: Were the same amounts of all of the control reagents used in each experiment?
Methods: Was the method exactly the same every time?
Equipment: Was the equipment used in each experiment?

Question 22

Subjectivity

Answer 22

-Consider the experiments where you had to read the volume of gas from the measuring cylinder…

-During the experiment, the gas was constantly being produced. That made the scale hard to read and so you could mention this in your evaluation.

-This tells the reader that whilst your results were gathered to the best of your ability, they are not without human error.

-Repeating an experiment will reduce the effect of subjectivity and make results more reliable.

Question 23

Amounts

Answer 23

Amounts usually refers to the controlled variables, but can refer to any aspect of reagents used in an experiment.

-When we investigated temperature we had to make sure surface area was the same. Was it? Did you make sure the surface area of the marble was kept the same? Probably no - so you need to mention this in your evaluation.

-The trend of your results will still be the same with ‘approximate’ amounts BUT if you were to repat it then it is unlikely that you would get exactly the same values

-This impacts repeatability (similarity of results obtained by the same person on the same day) and reproducibility (similarity of results obtained by different people on different days).

-Repeating an experiment will reduce the effect of natural variation and make results more reliable

Question 24

Method

Answer 24

-So far, when investigating rate we have had two methods of collecting results; collecting gas produced over time and tracking mass loss over time.

-Can we compare these results? How do we know whether 2 g/s represents a faster rate than 30cm^3/s?
If you used a different method are your results comparable?
This is an extreme case but even small changes to the method can impact results. This becomes more likely when someone else is trying to reproduce an experiment

Question 25

Equipment

Answer 25

The use of equipment can have a large effect on how PRECISE our data can be (how many decimal places on a balance? How precisely can we measure temperature on a 100C vs 50C thermometer?) and how ACCURATE our result is.

Choice of equipment needs to be appropriate for the needs of the experiment:
-If our measurements are not very precise then we can get lots of RANDOM ERROR occurring
-The wrong equipment can also cause SYSTEMATIC ERROR causing results to be invalid

Question 26

What happens when activation energy is lower?

Answer 26

-If it is lower, more collisions will occur with the required energy so the reaction will occur more quickly

Question 27

How does surface area affect rate of reaction?

Answer 27

-If we increase the surface area of a solid reactant, more reactant particles are exposed to each other, leading to an increase of the frequency of collisions (and hence the frequency of successful collisions
-This means that an increase in surface area results in a higher reaction rate

Question 28

How does temperature affect the rate of reaction?

Answer 28

If we increase the temperature:
1. The reactant particles will have more kinetic energy, and so
2. More particles will have sufficient energy to form products, and
3. Therefore the frequency of successful collisions (and hence reaction rate) increases

Question 29

How does concentration affect the rate of reaction?

Answer 29

Increasing the concentration means:
1. There are more reactant particles in a given volume of space, so
2. particles collide more frequently, so
3. successful collisions happen more frequently, increasing reaction rate

Question 30

How does the presence of a catalyst affect the rate of reaction?

Answer 30

-When a catalyst is present, the rate of reaction increases because the catalyst lowers the activation energy so more collisions will occur with enough energy (energy greater or equal to the activation energy) to react, so the reaction will occur faster (and hence the frequency of successful collisions increases)

Question 31

What does room temperature mean for chemical reactions?

Answer 31

The activation energy will be much lower

Question 32

What does a negative energy change mean?

Answer 32

There is a loss of energy from the system, so the reaction is exothermic.

Question 33

What does a positive energy change mean?

Answer 33

There is a gain in energy in the system and the reaction in endothermic.

Question 34

What should a graph title be?

Answer 34

A graph to show the effect of changing the (IV) on the (DV)

Question 35

How should an aim be written?

Answer 35

To determine the effect of changing the (IV) on the (DV) when (context)