The Rate And Extent Of Chemical Change

Question 1

Rate of Reaction

Answer 1

• how fast the reactants are changed into products

- vary from iron rusting to explosions

Question 2

How does the steepness of a graph show the rate of reaction

Answer 2

Steeper line, faster reaction

Question 3

What does a flat line on a graph show?

Answer 3

The reaction has stopped

Question 4

Collision Theory

Answer 4

• rate of reaction depends on collision frequency and energy transferred in each collision
• particles must have activation energy when they collide in order to react
• factors affecting rate of reaction must affect either collision energy or frequency

Question 5

What four factors affect rate of reaction?

Answer 5

Temperature
Concentration of solution/pressure of gas
Surface area
Catalysts

Question 6

How does increased temperature increase rate of reaction?

Answer 6

• particles all moving faster
• going to collide more frequently and with more energy
• more likely to have the activation energy and react

Question 7

How does increasing concentration/pressure increase the rate of reaction?

Answer 7

• particles are more closely packed together

- collisions between particles are more frequent

Question 8

How does increasing surface area increase the rate of reaction?

Answer 8

• more particles exposed
• more particles can react at once
• higher collision frequency

Question 9

How do catalysts increase the rate of reaction?

Answer 9

• speeds up reaction without being used up itself

- dear ease activation energy required

Question 10

Catalyst

Answer 10

Substance that increases the rate of a reaction without being used up

Question 11

Experiment: magnesium and HCl rate of reaction

Answer 11

• set volume of HCl in conical flask
• add magnesium ribbon and attach gas syringe to flask
• start stopwatch; take gas readings at regular intervals
• plot results in a table
• plot graph (time on x-axis, volume of gas produced on y-axis)

Question 12

Experiment: sodium thiosulphate and HCl rate of reaction

Answer 12

• both clear solutions: react to form a yellow precipitate of sulphur
• add set volume of dilute sodium thiosulphate to conical flask
• place flask on paper with a black cross drawn on it
• add dilute HCl and start the stopwatch
• time how long it takes for cross to disappear

Question 13

Equilibrium

Answer 13

Both reactions are happening at the same rate

Question 14

Reversible reactions

Answer 14

A + B <=> C + D

• concentrations of reactants fall, so backwards reaction speeds up and forwards reaction slows down
• eventually reach an equilibrium
• both reactions still happening with no overall effect
• equilibrium only reached in a closed system

Question 15

Closed system

Answer 15

• none of the products/reactants can escape

- nothing else can get in

Question 16

What conditions affect the position of equilibrium?

Answer 16

• temperature
• pressure
• concentration

Question 17

Le Chatelier’s Principle

Answer 17

• change conditions of reversible reaction at equilibrium
• system tries to counteract the change
• predict the effect of changes made to a closed reaction system

Question 18

How does a reversible reaction respond to changes in temperature?

Answer 18

• exothermic in one direction and endothermic in the other
• decrease temperature, equilibrium moves in exothermic direction to produce more heat and vice versa
• more products for exothermic reaction and vice versa

Question 19

How does a reversible reaction respond to changes in pressure?

Answer 19

• only affects equilibrium involving gases
• increase pressure; equilibrium tries to reduce it
• moves towards direction where there are less molecules of gas
• vice versa
• balanced symbol equation used to see which side has more molecules of gas

Question 20

How does a reversible reaction respond to changes in concentration?

Answer 20

• change concentration of reactants or products, system no longer in equilibrium
• system brings itself back to equilibrium
• increase concentration of reactants; system makes more products
• vice versa

Question 21

What does a steep line show in a rate of reaction graph?

Answer 21

The reaction is happening very quickly

Question 22

What two factors relating to collisions between particles influence the rate of reaction?

Answer 22

Collision Frequency

Energy of colliding particles

Question 23

Equation used to calculate mean rate of reaction

Answer 23

RoR = products formed / time
OR
RoR = reactants used / time

Question 24

Give three possible units for rate of reaction

Answer 24

Cm^3 / s
g / s
mol / s

Question 25

Three ways of measuring rate of reaction

Answer 25

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

Question 26

What is a tangent?

Answer 26

Straight line that touches the curve at one point but does not cross it

Question 27

What effect will decreasing the temperature have on a reversible reaction if the forward reaction is exothermic?

Answer 27

The equilibrium moves to the forward reaction

Question 28

How will the equilibrium position change if the pressure is increased?

Answer 28

• moves towards side with less molecules

Question 29

What effect will decreasing the concentration of the products for the forward reaction have on the equilibrium position in a reversible reaction?

Answer 29

Equilibrium moves to forward reaction to make more products