C6- Rate And Extent Of Chemical Change

Question 1

What is rate of chemical reaction

Answer 1

How fast reactants are changed into products

Question 2

Examples of rates of reaction

Answer 2

Slowest - rusting of iron
Medium - metal magnesium reacting with acid to produce bubbles
Quick - burning (explosions faster)

Question 3

Describe graphs for rates of reactions

Answer 3

Find reaction speed by recording amount of product formed or reactant used over time
Steeped line = faster rate of reaction
Overtime steepness decreases as reactant used up
Quickest reactions have steepest lines and flatten out quickest

Question 4

What must particles collide with in order to react

Answer 4

The activation energy

Question 5

What’s activation energy

Answer 5

Minimum energy required during collision of particles for them to react

Question 6

What does the rate of reaction depend on

Answer 6

Collision frequency of reacting particles - more collisions = faster reaction rate
Energy transferred during collision - collide with enough energy for successful reaction

Question 7

How does temperature affect rate of reaction

Answer 7

Temp increase = particles move faster
Collide more frequently which increases rate
Faster = more energy = more successful collisions

Question 8

How does concentration/pressure affect rate of reaction

Answer 8

Solution more concentrated = more particles knocking in same volume = collisions more frequent
Pressure increase = same particles in smaller space

Question 9

How does surface area increase rate of reaction

Answer 9

If reactant is solid, breaking into smaller pieces will increase SA to V ratio - same volume of solid , particles have more space = more collisions.

Question 10

How does a catalyst affect the rate of reaction

Answer 10

Different catalysts for different reactions
Catalysts decreases activation energy - provide alternate reaction pathway with lower activation energy.
Enzymes are biological catalysts - catalyse reactions I’m living things

Question 11

Equation for rate of reaction

Answer 11

Rate of reaction = amount of reactant used or product formed/time

Question 12

How does precipitation and colour change measure rate of reactions

Answer 12

Record visual changes - initial solution transparent and product is precipitate which clouds solution
Observe mark through solution and see how long it takes for it to disappear - can’t plot ROR graph

Question 13

How does change in mass measure rate of reaction

Answer 13

Measuring speed of reaction that produces a gas carried out with mass balance - as gas released, mass disappears on mass balance
Quicker reading drops = quicker reaction - most accurate but releases gas into room

Question 14

How is Volume of gas given off a measure of rate of reactions

Answer 14

Gas syringe to measure volume of gas given off - more gas given off = faster reaction
Syringe gives volume accurate to cm3
Measurements at regular intervals and plot ROR graph

Question 15

Equation to work out mean rate of reaction

Answer 15

Mean rate = change in y / change in x

Question 16

How do you find reaction rate at a specific point

Answer 16

Draw a tangent and find tangents gradient - rise/run

Question 17

What will reversible reactions reach

Answer 17

Will reach equilibrium

Question 18

What happens as reactants react

Answer 18

Their concentrations fall - forward reaction will slow down

Question 19

What happens as more products are made…

Answer 19

concentration rises and backwards reaction speeds up

After a while, the forward reaction will go at the same rate as the backward one - equilibrium

Question 20

What’s the forward and backward reaction

Answer 20

Forward: A-> ———-\ C >
B -> forward D>

Backward < A \———

Question 21

What happens at equilibrium

Answer 21

Both reactions are still happening, but there’s no overall effect > concentrations of reactants and products have balanced and won’t change

Question 22

Equilibrium only reached if…

Answer 22

Reversible reaction takes place in a closed system

Question 23

What does reactions at equilibrium not mean

Answer 23

Doesn’t mean amount of reactants and products are equal

Question 24

What happens if equilibrium is to the right or left

Answer 24

To the right - product concentration greater than reactants

To the left - reactant concentration greater than products

Question 25

What does the equilibrium position depend on

Answer 25

Temperature, pressure, concentration

E.g heating an equilibrium may cause a position change

Question 26

In reversible reactions, if reaction is Exothermic in one direction…

Answer 26

It will be endothermic in the other direction

Question 27

Energy transferred from surroundings by endothermic reaction is equal to….

Answer 27

Energy transferred to surroundings during exothermic reactions

Question 28

What is the Le Chateliers principle

Answer 28

Idea that if you change the conditions of a reversible reaction at equilibrium, the system will try to counteract that change

Question 29

Changes to temperature in equilibrium

Answer 29

If you decrease the temperature, equilibrium will move in exothermic direction to produce more heat
More products for exothermic reaction and fewer products for endothermic reaction

Question 30

Pressure changes in equilibrium

Answer 30

Increase pressure, equilibrium tries to reduce it - move in direction of fewer molecules
Decrease pressure, more in direction of more molecules
Balanced symbol equation to see which side has more gas moles

Question 31

Change of concentration in equilibrium

Answer 31

Increase concentration of reactants - system tries to decrease by making more products
Decrease concentration of products - reduce amount of reactants etc