topic 6 - rate and extent of chemical change

Question 1

whats the rate of a reaction

Answer 1

the rate at which the products get turned into reactants

Question 2

slow reactions

Answer 2

• rusting of iron

Question 3

typical rate reaction example

Answer 3

reaction btwn mag and acid - hydrogen bubbles

Question 4

fast rate of reaction example,

Answer 4

explosions - fireworks

Question 5

rate of reaction equation

Answer 5

products formed or reactants used cm^3 /time secs

Question 6

what are the axis for a graph to show rate of reaction

Answer 6

time on x axis
mass of reactants or volume of products formed on Y

Question 7

the collision theory

Answer 7

for particles to react they have to collide with each other with activation enegry and if there is less energy than this nothing will happen

Question 8

what does the collision theory depend on

Answer 8

1. amount of energy they have
2. frequency of collision

Question 9

4 factors that affect the rate of reaction

Answer 9

1. temp
2. concentration/pressure
3. surface area
4. catalyst

Question 10

how does temperature affect the rate of reaction

Answer 10

• temp increases
• particles gain more energy
• move faster and collide more frequently
• higher rate of reaction

Question 11

how does concentration or pressure affect the rate of reaction

Answer 11

if these increased there will be more particles per unit of volume there fore more frequent collision

Question 12

how does SA affect the rate of reaction

Answer 12

increase rate of reaction bc higher frequency of collision

Question 13

how does catalyst affect the rate of reaction

Answer 13

speeds up reaction but doesn’t get used up
- catalyst lowers activation energy by providing an alternative reaction pathway = higher proportion of successful collisions

Question 14

how do you calculate the actual rate of reaction at a particular point

Answer 14

find the gradient
- draw a line up from the time to the curve
- draw a tangent here
- change in y over change in x

Question 15

reversible reaction rates

Answer 15

the forwards and backward reactions can happen at different rates

Question 16

what happens when the reversible reaction reaches equilibrium

Answer 16

the forward and backward reactions even out and go at the exactly the same speeds and the concentration of the products and the reactions won’t change but that doesn’t mean they are the same

Question 17

where is the equilibrium with more products

Answer 17

more products = lies to the right

Question 18

where is the equilibrium with more reactants

Answer 18

more reactants = lies to the left

Question 19

when can eq only be reached

Answer 19

in a closed system - none of the reactants or products can escape

Question 20

what are the energy changes in a reversible reaction

Answer 20

Has to be exothermic in one direction and endothermic in the other

Question 21

whats the energy changes in the reaction of thermal decomposition of hydrated copper sulfate

Answer 21

hydrated copper sulfate <—> anhydrous copper sulfate + water
- forward is endothermic
- backward is exothermic

Question 22

what are the 2 points in la chatelier’s principle

Answer 22

• if you change the conditions of a reversible reaction at eq - the system will counteract that change
• therefore you can predict the effect of changes you make to a system

Question 23

a chatelier’s principle - changing TEMP

Answer 23

• decrease temp = eq goes to the exothermic side. therefore you get more products for the exothermic
• increase temp = eq goes to endothermic side. therefore you get more products for the endothermic side

Question 24

a chatelier’s principle - changing PRESSURE

Answer 24

GASES
- increase the pressure = eq tries to reduce and moves in direction with less moles of gas
- decrease pressure = eq tries to increase and moves direction with more mole of gas

Question 25

a chatelier’s principle - changing CONCENTRATION

Answer 25

• if you change the concentration the system is no longer at eq
• increase the conc of REACTANTS = system tries to decrease and makes more products
• decrease the conc of PRODUCTS = system tries to increase and reduces amount of reactants