Rate And Extent Of Chemical change

Question 1

How can you measure rate of reaction?

Answer 1

By measuring the quantity of a reactant used or the quality of product formed over time

Question 2

Equation to determine mean rate of reaction using a reactant

Answer 2

Mean rate = quantity of a reactant used ÷ time

Question 3

Equation to determine mean rate of reaction using product

Answer 3

Mean rate = quantity of products formed ÷ time

Question 4

How to calculate mean rate of reaction from a graph?

Answer 4

Rate (gradient) = change in y ÷ change in x

Question 5

Calculate the mean rate of reaction that produces 52 cm³ of gas in 2 minutes

Answer 5

52 ÷ 2 = 26cm³/min (could convert minutes to seconds so can use centimetres cubed per seconds units)

Question 6

How do you measure the amount of reactant or product made in a reaction?

Answer 6

Mass in g
Volume in cm³

Question 7

What are the units for rate of reaction?

Answer 7

g/s using mass
Or
cm³/s using volume

Question 8

What are the units for rate using moles?

Answer 8

mol/s

Question 9

How can you measure the rate of reaction from a graph at a specific time?

Answer 9

Draw a tangent and determine the gradient

Question 10

When drawing a tangent, how should the ruler be positions on the graph?

Answer 10

Place a ruler on the curve at the point where you want to know the slope. The space between the ruler and the curve should be equal on both sides of the point

Question 11

What does the steepness of the slope on a rate graph tell you?

Answer 11

How fast the reaction is, the steeper of the slope, faster the reaction

Question 12

How can you tell from a rate graph that the reaction has finished

Answer 12

The graph becomes flat

Question 13

How can you measure rate?

Answer 13

Loss in mass of reactants or
Volume of gas produced or
Time for a solution to become opaque (cloudy) or coloured

Question 14

What piece of equipment can you use to measure the volume of gas made?

Answer 14

Gas syringe or “ overwater” using an upturned, measuring cylinder in a water trough

Question 15

What are factors can affect the rate of a chemical reaction?

Answer 15

Concentration
Pressure
surface area
Temperature
Catalyst

Question 16

What is collision theory?

Answer 16

Reactants must collide with enough energy (activation energy)

Question 17

What is activation energy?

Answer 17

The minimum amount of energy of the particles must have to react

Question 18

What must particles have when they collide?

Answer 18

Sufficient amount of energy (activation energy)

Question 19

What does increasing temperature do in terms of collisions?

Answer 19

Rate increases, because particles move faster
So more frequent collisions
And more particles are colliding with energy greater than activation energy

Question 20

What does increasing concentrations do in terms of collisions?

Answer 20

More particles in a given volume
More frequent successful collisions

Question 21

How can you increase the surface area of a solid?

Answer 21

Break up the solid into small pieces/make it into a powder

Question 22

What does increasing pressure do in terms of collisions?

Answer 22

Particles are moves closer together
More frequent, successful collisions

Question 23

What is a catalyst?

Answer 23

A substance which increases the rate of chemical reactions
But are not used up during the reaction
Different reactions need different catalysts

Question 24

What is an enzyme?

Answer 24

A biological catalyst

Question 25

How do catalysts increase the rate of reaction?

Answer 25

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

Question 26

Are catalysts included in chemical equations

Answer 26

No

Question 27

What is a reversible reaction? What symbol is used to represent this?

Answer 27

The products of the reaction can react to produce the original reactants ⇌

Question 28

Why does the amount of products and reactants remain the same equilibrium?

Answer 28

The rate of forward reaction is equal to the rate of backward to reaction So the concentrations of products and reactants. Stay constant.

Question 29

An equation to show the reversible reaction when ammonium chloride is heated

Answer 29

Ammonium chloride ⇌ ammonia + hydrogen chloride —> heat <— cool

Question 30

How does a reaction reach equilibrium?

Answer 30

When a reversible reaction occurs in a closed system and the forward and backwards reactions happen at exactly the same rate

Question 31

What is a closed system?

Answer 31

When it is sealed, products or reactants, cannot enter or leave

Question 32

How can you change the direction of a reversible reaction?

Answer 32

By changing are the conditions of: Temperature Pressure Concentration

Question 33

If a reversible reaction is exothermic in one direction, What will the opposite direction be?

Answer 33

Endo thermic

Question 34

What is the amount of energy like in both directions in a reversible reaction?

Answer 34

The same

Question 35

An equation to show how hydrated copper sulphate can be heated to give anhydrous copper sulphate

Answer 35

Hydrated copper sulfate (blue) ⇌ anhydrous copper sulphate (white) + water

Question 36

What is equilibrium

Answer 36

When the forwards and reverse reactions happen at exactly the same rate (when in a closed system so the reactants abs products can’t escape from the reactants)

Question 37

What is Le Chateliers principal?

Answer 37

At equilibrium, if the conditions change it will shift to oppose these changes (it wants to try and get back to equilibria again).

Question 38

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

Answer 38

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

Question 39

What happens when the concentration of reactants are increased?

Answer 39

More products will be made to get rid of extra reactants added

Question 40

What happens when the concentration of the products are decreased?

Answer 40

More reactants will react to get more products again

Question 41

What happens if the temperature is increased

Answer 41

The equilibrium will always move in the endothermic direction

Question 42

What happens if the temperature is decreased?

Answer 42

The equilibrium will always move in the exothermic direction

Question 43

What happens if the temperature is increased for an endothermic reaction?

Answer 43

It was shift in favour of the endothermic reaction as it wants to cool back down

Question 44

What happens if the temperature is decreased for an endothermic reaction?

Answer 44

It will shift in favour of the exothermic reaction as it wants to heat back up

Question 45

What happens if the temperature is increased for an exothermic reaction?

Answer 45

It will shift in favour of the endothermic reaction as it wants it to cool back down

Question 46

What happens if the temperature is decrease are an exothermic reaction

Answer 46

It will shift in favour of the exothermic reaction as it wants to heat back up

Question 47

If a change in pressure occurs, what do you look at?

Answer 47

The number of GASEOUS MOLES on reactants vs products Eg N2(g) + 3H2(g) ⇌ 2NH3(g) There are four moles of gas on the reactant side There are 2 moles of gas on the products side

Question 48

What happens if pressure is increased in an equilibrium

Answer 48

Equilibrium shift towards the side with the least number of gaseous molecules

Question 49

What happens if pressure is decreased in an equilibrium

Answer 49

Equilibrium will shift towards the side with the most number of gaseous molecules

Question 50

What affect does pressure have if the same number of moles in the reactants and the products

Answer 50

None, no affect

Question 51

What effect does catalyst have on position of an equilibrium?

Answer 51

None as speeds up both the rate of forwards and backwards reactions equally