Rate and Extent of Chemical Change

Question 1

Rate of a chemical reaction

Answer 1

How fast reactants are turned into products

Question 2

What a steeper line mean on graph of rate of reaction

Answer 2

Faster rate of reaction

Question 3

What will happen to every line of rate of reaction graph

Answer 3

It will become less steep eventually as reactants are used up

Question 4

What do flat lines show on rate of reaction graph

Answer 4

Reaction has finished

Question 5

What do fastest reactions look like in rate of reaction graph

Answer 5

• steepest lines
• become flat in least time

Question 6

Collision theory

Answer 6

• more collisions means faster rate of reaction
• particles must collide with enough energy for collision to be successful

Question 7

Collision theory - what happens when particles collide

Answer 7

Energy is transferred

Question 8

Activation energy

Answer 8

Minimum amount of energy particles need to break bonds in reactants to start reaction

Question 9

Factors affecting rate of reaction

Answer 9

• temperature
• concentration of solution or pressure of gas
• surface area
• presence of catalyst

Question 10

How does temperature affect rate of reaction

Answer 10

• increasing temperature increases rate of reaction
• temperature increases - particles move faster
• faster movement - more frequent collisions + more collisions with enough energy to make reaction happen

Question 11

How does concentration of solution affect rate of reaction

Answer 11

• increasing concentration increases rate of reaction
• more particles in same volume of water/solvent
• more frequent collisions

Question 12

How does gas pressure affect rate of reaction

Answer 12

• increasing pressure increases rate of reaction
• more particles in smaller space
• more frequent collisions

Question 13

How does surface area affect rate of reaction

Answer 13

• increasing SA:V increases rate of reaction
• for same volume of solid, particles around it will have more area to work on
• solid reactants should be broken into smaller pieces

Question 14

How does presence of catalyst affect rate of reaction

Answer 14

• using catalyst increases rate of reaction
• substance that speeds up rate of reaction without being used up in reaction itself (not part of reaction)
• decrease activation energy by providing alternative reaction pathway with lower activation energy

Question 15

How to calculate mean rate of reaction

Answer 15

• quantity of reactant used / time taken
• quantity of product formed / time taken

Question 16

units of rate of reaction

Answer 16

• cm³/s
• g/s
• mol/s

Question 17

Ways of measuring rate of reaction

Answer 17

• colour change
• change in mass
• volume of gas given off

Question 18

When can rate of reaction be measured with colour change

Answer 18

When initial solution is transparent and product is precipitate that clouds solution - turning it opaque

Question 19

Measuring rate of reaction - colour change

Answer 19

• place laminated cross on surface
• place flask over cross
• observe + time how long it takes for cross to disappear
• faster disappearance = faster reaction rate

Question 20

Problems with measuring rate of reaction with colour change

Answer 20

• subjective results - people may disagree on exact point mark ‘disappears’ when solution changes colour
• can’t plot graph of rate of reaction

Question 21

How to measure rate of reaction with change in mass

Answer 21

• place flask on electric balance
• as gas released - mass on balance drops
• faster balance drops - faster reaction rate

Question 22

When can rate of reaction be measured with change in mass

Answer 22

When reaction produces gas

Question 23

Safety procaution for measuring rate of reaction with change in mass

Answer 23

Put cotton wool at top of flask to stop acid spitting out but allow gas to escape

Question 24

Advantage of measuring reaction rate with change in mass

Answer 24

• most accurate of 3 methods
• can plot results on graph

Question 25

Disadvantage of measuring rate of reaction with change in mass

Answer 25

Gas being released straight into room

Question 26

How to measure rate of reaction with volume of gas given off

Answer 26

- place bung + gas syringe in flask - gas syringe measures volume of gas produced in reaction - more mass given off in time interval - faster reaction rate

Question 27

When can rate of reaction be measured with volume of gas given off

Answer 27

When reaction produces gas

Question 28

Advantage of measuring rate of reaction with volume of gas given off

Answer 28

- gas syringes accurate - usually give volume to nearest cm³ - can plot results on graph

Question 29

Disadvantage of measuring rate of reaction with volume of gas given off

Answer 29

Reaction too vigorous - can blow plunger out of end of syringe

Question 30

How to find mean rate of reaction from graph

Answer 30

Gradient of that interval / whole reaction

Question 31

How much of graph to find gradient of when calculating mean rate of whole reaction

Answer 31

From start to when graph becomes flat (reaction has already finished)

Question 32

How to find rate of reaction at a particular point from graph

Answer 32

- draw tangent - find gradient of tangent

Question 33

Reversible reaction equation

Answer 33

A + B ⇌ C + D

Question 34

Reversible reaction

Answer 34

Reaction where products can react to form reactants and will reach dynamic equilibrium

Question 35

How does a reversible reaction reach equilibrium

Answer 35

- as reactants react, concentrations fall - forward reaction slows down - as more products made, concentrations rise - backward reaction speeds up - after while - forward + backward reaction happening at same rate (equilibrium)

Question 36

What happens at equilibrium

Answer 36

Both reactions still happening but no overall effect, concentrations of reactants/products reached balance, won't change

Question 37

What must conditions be for equilibrium to be reached

Answer 37

Reaction must take place in closed system

Question 38

Why can position of equilibrium lie to left/right

Answer 38

Amount of reactants/products not equal

Question 39

What does it mean if equilibrium lies to right

Answer 39

Concentration of products greater than concentration of reactants

Question 40

What does it mean if equilibrium lies to left

Answer 40

Concentration of reactants greater than concentration of products

Question 41

What determines position of equilibrium

Answer 41

- temperature - pressure if involving gases - concentration of reactants and products

Question 42

If 1 direction of reaction is endothermic what must other direction be

Answer 42

Exothermic

Question 43

If 1 direction of reaction is exothermic what must other direction be

Answer 43

Endothermic

Question 44

Relationship between energy transferred in endo/exo in reversible reaction

Answer 44

Energy transferred from surroundings in endothermic equal to energy transferred to surroundings in exothermic

Question 45

Le Chatelier's Principle

Answer 45

If you try to change conditions of reversible reaction at equilibrium, system will try to counteract change

Question 46

What happens if you decrease temperature of reversible reaction

Answer 46

- equilibrium will move in exothermic direction to produce more heat - more products for exothermic reaction, fewer products for endothermic reaction

Question 47

What happens if you increase temperature of reversible reaction

Answer 47

- equilibrium will move in endothermic direction to try decrease it - more products for endothermic reaction, less products for exothermic reaction

Question 48

What happens if you increase pressure of reversible reaction

Answer 48

Equilibrium tried to reduce it by moving in direction where there are fewer gas molecules

Question 49

What happens if you decrease pressure of reversible reaction

Answer 49

Equilibrium tries to increase it by moving in direction where there are more gas molecules

Question 50

What happens if you change concentration of reactants/products in reversible reaction

Answer 50

- system no longer at equilibrium - will respond to bring it back

Question 51

What happens if you increase concentration of reactants in reversible reaction

Answer 51

System makes more products to decrease it

Question 52

What happens if you decrease concentration of products in reversible reaction

Answer 52

System less reactants to increase it