C8.1 - C8.9 - Rates And Equalibrian✔️

Question 1

What happens when a reaction reaches equilibrium in a closed system?

Answer 1

At equalibrian the rate of the forward reaction equals the rate of the reverse reaction

Question 2

What does it mean if a reaction is in a closed system?

Answer 2

Closed system - no reactants or products can get out

Question 3

What is a reversible reaction?

Answer 3

The products of the reaction can react to re-form the original reactants

Question 4

Define Le Châteliers Principle?

Answer 4

noticed that whenever a change in conditions is introduced to a system at equilibrium the postion of equalibrium shifts so as to cancel out the change - the change in conditions can be changes in concentration,pressure or tempertaure

Question 5

Le Châteliers Principle states that changes in …….. effect the position of equalibrium?

Answer 5

the change in conditions can be changes in concentration,pressure or tempertaure which will shift the position of equalibrium

Question 6

Why is Le Châteliers Principle important in the chemical industry?

Answer 6

Chemists need to find the conditions that give as much products as possible in the shortest time so it is economical

Question 7

2 ways to work out the rate of a chemcial reaction?

Answer 7

-the reactants are used up as they make products

-the products of the reaction are made

Question 8

Finding out what 2 things…. allows you to work out the rate of a chemical reaction?

Answer 8

by finding out how quickly:

-the reactants are used up as they make products

-the products of the reaction are made

Question 9

How do you calculate the rate of reaction at a specific time on a graph?

Answer 9

Draw the tangent to the curve and caculate its gradient (change in y / change in x) - the steeper the gradient the faster the reaction

Question 10

5 main factors which effect the rate of a reaction?

Answer 10

-temperature
-surface area of solid reactants
-concentration of reactants in solution
-pressure of reacting gases
-presence of catalyst

Question 11

Explain the collision theory?

Answer 11

Reactions can only take place when the particles (atoms,ions,molecules) reactants come together - and bump into each other and collide with enough energy to cause a reaction to take place

Question 12

Define what activation energy is?

Answer 12

The minimum amount of energy that particles must have before they can react

Question 13

3 ways you can increase the chance of a reaction?

Answer 13

-increasing the concentration of reactants in solutions

-increasing pressure of reacting gases

-increasing surface area of solid rectants

Question 14

How will temperature increase rate of reaction?

Answer 14

Increases the frequency of collisions and makes the collisions more energetic which will result in an increased rate of reaction becasue a higher proportion of particles have energy greater than the activation energy - because heating a substance transfers energy to its particles which means they move faster

Question 15

Why does increasing the surface area increase the rate of reaction?

Answer 15

More particles of the solid are exposed and able to react at any given time and are in contact with reacting particles

Question 16

Equation for working out the rate of a reaction?

Answer 16

Mean rate of reaction = quanity of reactant used / time

Question 17

Effect of increasing pressure?

Answer 17

Increasing pressure of reacting gases also increases the frequeny of collisions and so increases the rate of reaction

Question 18

Effect of increasing concentration?

Answer 18

Increasing concentration of reactants in solutions increases the frequency of collisions between the particles, and so increases the rate of reaction

Question 19

What are catalysts?

Answer 19

Changes the rate of chemical reactions but are not used up during the reaction - different reactions need different catalysts (enzymes act as catalysts in biological systems)

Question 20

How do catalysts increase the rate of a chemical reaction?

Answer 20

Catalysts provide a different pathway for the reaction that has a lower activation energy

Question 21

What are 2 disadvantages of catalysts?

Answer 21

• often very expensive metals - gold, platinum and palladium
• catalysts will eventually become ‘poisoned’ so that they do not work anymore

Question 22

What are 3 advantages of catalysts?

Answer 22

• better for the enviorment - less fossil fules used to create the high temperature normally needed
• more economical - cost less and less energy is needed
• not used up in the reaction - can be used to speed up a reaction over and over again

Question 23

How do catalysts benefit the enviorment?

Answer 23

Catalysts can result in the ability to operate at lower temperatures so less fossil fuels are burnt and it also stops more carbon dioxide entering the atmosphere helping combat climate change

Question 24

Explain how catalysts become ‘poisend’?

Answer 24

Impurities in the reaction mixture combine with the catalyst and eventually they stop working properly

Question 25

What does changing the conditions result in for reversible reactions? give and example of the reaction with ammonium chloride?

Answer 25

The direction of the reversible reaction eg:

                             (heat) Ammonium chloride ⇌ ammonia  +hydorgen chloride                   (cool)

Question 26

If a reversible reaction is exothermic in one direction in the opposite direction it will be ….? Give an example using hydrated copper sulfate?

Answer 26

Endothermic with the same amount of energy transferred in each case
Example:

                              (endothermic) Hydrated copper sulfate ⇌ anhydrous copper sulfate + water        (exothermic)

Question 27

What is the result when a reversible reaction occurs in apparatus which prevents the escape of reactants and products?

Answer 27

Equilibrium is reached when the forward and reverse reactions occur at exactly the same rate

Question 28

What happens if the concentration of one of the reactants or products is changed?

Answer 28

The system is no longer at equalibrium and the concentrations of all the substances will change until equilibrium is reached again

Question 29

What happens if the concentration of a reactant is increased?

Answer 29

More products will be formed until equalibrium is reached again

Question 30

What happens if the concentration of a reactant is decreased?

Answer 30

More reactants will react until equalibrium is reached again

Question 31

What happens if the temperature of a system at equalibrium is increased in both exothermic and endothermic reactions?

Answer 31

• relative amount of products at equalibrium increased for endothermic reaction
• relative amount of products at equalibrium decreases for exothermic reaction

Question 32

What happens if the temperature of a system at equalibrium is decrease in both exothermic and endothermic reactions?

Answer 32

• the relative amount of products at equalibrium decreases from an endothermic reaction
• the relative amount of products at equalibrium increases for an exothermic reaction

Question 33

What is the effect of an increase in pressure on the position of equilibrium?

Answer 33

An increase in pressure causes the equlibrium position to shift towards the side with the smaller number of molecules as shown by the symbol equation for that reaction

Question 34

What is the effect of an decrease in pressure on the position of equilibrium?

Answer 34

A decrease in pressure cause the equalibrium position to shift towards the side with the larger number of molecules as shown by the symbol equation for that reaction

Question 35

How can yoou change the relative amount of products formed at equalibrium?

Answer 35

Changing the temperatue at which you carry out the reversible reaction - you can plan to get more of the products and less of the reactants

Question 36

What can Le Chatelier’s Prinicle be used for?

Answer 36

The effects of changing conditions on a system can be predicted using this principle