Rate + Extent Of Chemical Change

Question 1

When do chemical reactions occur?

Answer 1

When reacting particles collide with each other with sufficient energy

Question 2

What is activation energy?

Answer 2

The minimum amount of energy required to cause a reaction

Question 3

What four factors effect the rate of reaction?

Answer 3

Temperature, surface area, concentration and catalysts

Question 4

How does temperature effect the rate of reaction?

Answer 4

In a hotter reaction mixture, the particles have more energy so move quicker, increasing the chance of a successful collision and the energy with which they collide with

Question 5

How does concentration effect the rate of reaction?

Answer 5

At higher concentrations, there are more particles in a smaller space so there are more successful collisions

Question 6

How does increasing the pressure of gases increase the rate of reaction?

Answer 6

It causes there to be more particles in a smaller space so they collide more frequently

Question 7

How does surface area effect the rate of reaction?

Answer 7

Smaller pieces of a solid reactant have a large surface area in relation to there volume. More particles are exposed to others so a reaction happens faster

Question 8

When the graph showing the progress of a chemical reaction goes flat, what has happened?

Answer 8

All the reactants have been used up

Question 9

How can we find the rate of reaction at a given time on a graph that shows the progress of a chemical reaction?

Answer 9

Drawing a tangent and finding the gradient of it

Question 10

What is a catalyst?

Answer 10

A substance that increases the rate of reaction without being used up itself

Question 11

Are catalysts included in the chemical equation for a reaction?

Answer 11

No because they aren’t a product or reactant

Question 12

What does a catalyst do to the activation energy to increase rate of reaction?

Answer 12

Reduces it by finding an alternate reaction pathway

Question 13

Name a catalyst in a biological system

Answer 13

Enzymes

Question 14

Why is increasing the rate of reaction important in industry?

Answer 14

Helps reduce cost

Question 15

What is a reversible reaction?

Answer 15

The products can react to produce the original reactants

Question 16

Closed system

Answer 16

No reactants are added and no products are removed from the reaction

Question 17

What is equilibrium?

Answer 17

When in a closed system, the rate of the forwards reaction is equal to that of the backwards reaction

Question 18

What is Le Chatelier’s principle?

Answer 18

That if a system in equilibrium is subjected to change, it will shift to combat the change

Question 19

What happens in a reaction at equilibrium if the temperature is raised?

Answer 19

It will shift in the endothermic direction

Question 20

What happens in an exothermic reaction at equilibrium if temperature is lowered?

Answer 20

It will shift in the exothermic direction

Question 21

What happens in an increase of pressure in a reaction containing gases at equilibrium?

Answer 21

It favours which ever side produces less gas

Question 22

What happens in an decrease of pressure in a reaction containing gases at equilibrium?

Answer 22

It the favours the side that produces most gas

Question 23

Which direction will a reaction at equilibrium shift if the concentration of one of the reactants is increased?

Answer 23

To the left

Question 24

Which direction will a reaction at equilibrium shift if the concentration of one of the products is increased?

Answer 24

To the right

Question 25

Rate of reaction equation

Answer 25

amount of reactant used or product formed/ time

Question 26

Apart from grams, what else can a reactant be measured in?

Answer 26

Moles

Question 27

Concentration equation

Answer 27

Amount of substance (mol)/volume (dm3)

Question 28

What are the three different ways to measure the rate of reaction? (Experiments)

Answer 28

• precipitation and colour change
• change in mass
• volume of gas given off

Question 29

Precipitation and colour change to find rate of reaction

Answer 29

1) You can record the visual change in a reaction if the initial solution is transparent and the product is a precipitate which clouds the solution (it becomes opaque).
2) You can observe a mark through the solution and measure how long it takes for it to disappear-the faster the mark disappears, the quicker the reaction
3) If the reactants are coloured and the products are colourless (or vice versa), you can time how long it takes for the solution to lose (or gain) its colour.
4) The results are very subjective- different people might not agree over the exact point when the mark ‘disappears’ or the solution changes colour. Also, if you use this method, you can’t plot a rate of reaction graph from the results.

Question 30

Change in mass to find rate of reaction

Answer 30

1) Measuring the speed of a reaction that produces a gas can be carried out using a mass balance.
2) As the gas is released, the mass disappearing is measured on the balance.
3) The quicker the reading on the balance drops, the faster the reaction.
4) If you take measurements at regular intervals, you can plot a rate of reaction graph and find the rate quite easily.
5) This is the most accurate of the three methods desecribed because the mass balance is very accurate. But it has the disadvantage of releasing the gas straight into the room.

Question 31

Volume of gas given off to find rate of reaction

Answer 31

1) This involves the use of a gas syringe to measure the volume of gas given off
2) The more gas given off during a given time interval, the faster the reaction.
3) Gas syringes usually give volumes accurate to the nearest cm* so they’re quite accurate. You can take measurements at regular intervals and plot a rate of reaction graph using this method too You have to be quite careful though - if the reaction is too vigorous you can easily blow the plunger out of the end of the syringe.

Question 32

Volume of gas produces to find rate of reaction experiment

Answer 32

1) Start by adding a set volume of dilute hydrochloric.acid to a conical flask
2) Now add some magnesium ribbon to the acid and quickly attach an empty gas syringe to the flask
3) Start the stopwatch. Take readings of the yolume of gas in the gas syringe at regular intervals
4) Plot the results in a table.
5) Now you can plot a graph with time on the x-axis and vol of gas produced on the y-axis

Question 33

Precipitation and colour change to find rate of reaction experiment

Answer 33

1) These two chemicals are both clear solutions. They react together to form a yellow precipitate of sulfur.
2) Start by adding a set volume of dilute sodium thiosulfate to a conical flask.
3) Place the flask on a piece of paper with a black cross drawn on it.
4) Add some dilute HCl to the flask and start the stopwatch.
5) Now watch the black cross disappear through the cloudy sulfur and time how long it takes to go.