rate and extent of chemical

Question 1

what formula can be used to calculate the rate of a chemical reaction

Answer 1

rate of reaction formulas:

• amount of reactant used / time
• product formed / time
• moles of reactant used / time
• moles of product formed / time

Question 2

What is the equation to find out the mean rate of a reaction?

Answer 2

Mean rate of reaction = quantity of reactant used / time taken

Question 3

What are the five factors that affect the rate of a chemical reaction?

Answer 3

• Temperature
• Surface area of solid
• Concentration of solutions
• Pressure of gases
• Presence of catalyst

Question 4

What is collision theory?

Answer 4

states that chemical reactions can only take place when reacting particles collide with each other
- the collisions must have sufficient energy

Question 5

How can you make reactions more likely to happen between reactant particles?

Answer 5

• Increase the frequency of reacting particles colliding with each other
• Increase the energy they have when they collide

Question 6

How does a bigger SA:V ratio affect the rate of a chemical reaction?

Answer 6

Increases it, because the frequency of collisions between the reacting particles increases - if solid reactants are in smaller pieces they have a greater surface area

Question 7

How does increasing the concentration of a solution affect the rate of a reaction?

Answer 7

Increases it, as it increases the frequency of collisions between particles

Question 8

How does increasing gas pressure affect the rate of a reaction?

Answer 8

Increases it, as the number of gas molecules in the same volume is increased and so increases the frequency of succesfull collision and therefore increases rate of reaction

Question 9

What is a catalyst?

Answer 9

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

Question 10

How do catalysts work?

Answer 10

They increase rates of reaction by providing an alternative reaction pathway for reactants and lowering the activation energy the particles therefore need less energy to surpass the activation energy, so there are more successful collisions

Question 11

What are advantages of catalysts?

Answer 11

they allow us to carry out reactions quickly without raising the temperature, saving money
- they can also be reused
- different reactions need different catalysts

Question 12

What is a reversible reaction?

Answer 12

A chemical reaction where the products can react to produce the original reactants again

Question 13

If a chemical reaction is endothermic, what is the reverse reaction?

Answer 13

Exothermic

Question 14

What is dynamic equilibrium?

Answer 14

in a closed system when the forward and backward of a reversible reaction are happening at the same rate and the concentrations of reactants and products remain constant

Question 15

What is Le Chatelier’s principle?

Answer 15

If a system is at equilibrium and a change is made to any of the conditions, the system responds to counteract the change

Question 16

What happens if the temperature of a reaction at equilibrium is decreased or increased?

Answer 16

if the temperature of a system at equilibrium is increased:
- the products of the endothermic reaction will increase
- the products of the exothermic reaction will decrease
- the equilibrium will shift towards the product of the endothermic reaction, to decrease the temperature

if the temperature of a system at equilibrium is decreased:
- the products of the endothermic reaction will decrease
- the products of the exothermic reaction will increase
- the equilibrium will shift towards the product of the exothermic reaction to increase the temperature - The exothermic reaction would be favoured

Question 17

What would happen if the concentration of reactants in a reaction at equilibrium was increased?

Answer 17

• if the concentration of one of the reactants or products is changed, the system is no longer at equilibrium
• the concentrations of all the substances will change until equilibrium is reached again
• if you increase the concentration of the reactant, more of the product will be formed
• if you decrease the concentration of the product, more of the reactant will react
• The reaction would favour the other direction, shifting the equilibrium to generate more products

Question 18

What would happen if the pressure of gases in a reaction at equilibrium was increased?

Answer 18

for gaseous reactions at equilibrium:

• An increase in pressure = cause the equilibrium position to shift towards the side with the smaller number of molecules
• A decrease in pressure = cause the equilibrium position to shift towards the side with the larger number of molecules
• if the number of molecules on both sides is equal, changing the pressure will have no effect on the equilibrium position

Question 19

describe the effect of a catalyst on the position and rate of equilbrium

Answer 19

No, catalysts do not affect the position of equilibrium; only the rate of the forward/backward reactions are sped up equally ( equilibrium achieved faster )

Question 20

explain the shape of the graph for a reactant product graph

Answer 20

• reactions are rapid initially because we have a large number of reactant molecules = there will be a large number of collisions per second
• over time reactions slow down because the number of reactant molecules are running out = there is a smaller number of collisions per second
• reaction stops because all of the reactant molecules have run out = number of collisions per second = 0

Question 21

what are 3 ways of measuring rate of reaction

Answer 21

• loss in mass of reactants
• volume of gas produced
• time for a solution to become opaque

Question 22

what is an enzyme

Answer 22

a molecule that acts as a catalyst in a biological system

Question 23

Using a graph, how can you tell if it has a faster reaction

Answer 23

• higher concentration = faster reaction
• easy to see because line is steeper

Question 24

what is the result of the product if there is a higher concentration of reactant

Answer 24

more product at the end - as there are more reactant molecules at the start and so there are more reactant particles moving together and there will be more collision so reaction rate increased

Question 25

Describe the required practical using sodium thiosulfate - disappearing cross experiment

Answer 25

sodium thiosulfate solution + hydrochloric acid --> sulfur - sulfur makes the solution go cloudy ( also known as turbidity) 1) use measuring cylinder to measure 10cm³ of sodium thiosulfate solution into a conical flask 2) place conical flask on printed black cross 3) add 10cm³ of hydrochloric acid into conical flask 4) swirl solution and start a stopwatch 5) look down at the top of the flask, after some time the solution should start to turn cloudy 6) stop the clock when you no longer see the cross 7) carry out experiment again, with lower concentrations of sodium thiosulfate solution 8) repeat whole experiment, and calculate mean values for each concentration of solution

Question 26

how can we determine if a measurement if reproducible

Answer 26

- if it can be repeated by another person or using a different technique or equipment and still get the same result

Question 27

what is an issue with the disappearing cross experiment

Answer 27

different people have different eyesights = some people can see cross for longer than others so they might not get the same results

Question 28

describe the effect of concentration on reaction rate - using magnesium

Answer 28

magnesium + hydrochloric acid -> magnesium chloride + hydrogen - the reaction produces hydrogen gas = allows us to measure the volume of hydrogen gas produced 1) use measuring cylinder to measure 50cm³ of hydrochloric acid into a conical flask 2) attach conical flask to a bung and delivery tube, and place the tube in a container full of water 3) place upturned measuring cylinder also filled with water over the delivery tube 4) add 3cm strip of magnesium to hydrochloric acid, and start a stopwatch 5) the reaction produces hydrogen gas, which is trapped in the measuring cylinder 6) every ten seconds, measure volume of hydrogen gas in measuring cylinder, and continue until no more hydrogen is given off 7) repeat experiment with different concentrations of hydrochloric acid - the greater the concentration of a chemical in a reaction, the faster the reaction takes place

Question 29

what does frequency mean

Answer 29

the number of successful collision per second

Question 30

the particles in solution can only react with ?????????

Answer 30

particles on the surface of the solid

Question 31

which block has a greater surface area to volume ratio: the smaller sized blocks or larger sized blocks

Answer 31

smaller sized blocks have a greater SA: V ratio = more particles on the surface = more collisions per second = increases rate of reaction

Question 32

what is the activation energy

Answer 32

the minimum amount of energy that the particles must have in order to react

Question 33

what does the size of the arrow on the particles show

Answer 33

shows the energy of each particle

Question 34

what would be the result if two particles which have only a small amount of energy collide with eachother

Answer 34

- Because they have low energy, they cannot overcome the activation energy barrier = not collide successfully and no reaction would occur

Question 35

what would be the result if two particles which have a large amount of energy collide with each other

Answer 35

- they have enough energy to overcome the activation energy barrier and collide successfully = reaction would take place

Question 36

What will increasing the temperature do to the rate of reaction and why

Answer 36

increases it - as increasing the temperature increases the energy of the particles - because the paticles now have more energy they now move faster = increases the frequency of collision and there will be a greater number of collisions per second AND Each collision now has more energy = more particles can overcome the activation energy barrier and collide successfully

Question 37

what is the relationship between rate of reaction and temperature

Answer 37

directly proportional to each other as RATE OF REACTION INCREASES WITH TEMPERATURE

Question 38

when ammonium chloride is heated what are the products

Answer 38

ammonia + hydrogen chloride

Question 39

when ammonia + hydrogen chloride are cooled what is the product

Answer 39

ammonium chloride

Question 40

what type of reaction does ammonium chloride use

Answer 40

reversible reaction - the products can react to reform the original reactants

Question 40

how can the direction of reversible reactions be changed

Answer 40

by changing the conditions eg the reaction can go forwards by heating and or the reaction can go backwards by cooling

Question 41

what is the product when hydrated copper sulfate is heated

Answer 41

reacts to form anhydrous copper sulfate ( which is white ) and also produces water

Question 42

what is the equation linking hydrated copper sulfate and heat

Answer 42

hydrated copper sulfate ->--<( heat ) anhydrous copper sulfate ( white ) + water

Question 43

what type of reaction occurs when a substance is heated

Answer 43

endothermic - because energy is being put in

Question 44

if a reversible reaction is exothermic in one direction what is the reaction in the other direction

Answer 44

endothermic

Question 45

what happens to the energy transferred in an forward and backward endothermic and exothermic reaction

Answer 45

the same amount of energy is transferred in each case

Question 46

what is equilibrium

Answer 46

the point at which the forward and reverse reactions take place at exactly the same rate