C6 rate and extent of chemical change

Question 1

what is the formula to calculate the mean rate of reaction?

Answer 1

quantity of reactant used / time taken

Question 2

on a rate graph, why does the line flatten out?

Answer 2

All the reactants has reacted so the reaction stops

Question 3

on a rate graph. what does it mean when the line is steeper?

Answer 3

the steeper the line, the faster the reaction

Question 4

how do you calculate the rate on a curved part of a line on a rate graph?

Answer 4

-pick a point
-draw a tangent
-make a triangle
-work out length of shorter sides
-use dy/dx to get the rate

Question 5

why do chemical reactions happen (collision theory)?

Answer 5

reactant particles collide with enough energy (activation energy) to break the bonds between the reactant atoms (successful collisions)

Question 6

if the pressure/concentration of the reactant is increased, why does the rate increase?

Answer 6

-there are more reacting particles in the same volume
-particles will collide more frequently
-more successful collisions
-so the rate increases

Question 7

if the temperature of reactants is increased then why does the rate increase?

Answer 7

-higher temp so more energy
-particles move faster so they collide with more force/energy
-more frequent collisions
-more collisions with energy >= activation energy
-more frequent successful collisions
-so rate increases

Question 8

if the surface area increases then why does the rate increase?

Answer 8

-more particles are exposed to the other reactant
-more frequent collisions per unit of time
-more successful collisions
-so the rate increases

Question 9

what is the effect of a catalyst of rate

Answer 9

-a catalyst provides an alternative route for the reaction with a lower activation energy needed for a successful reaction
-but there are more successful collisions
-so the rate increases

Question 10

describe a method to investigate the effect of the concentration of sodium thiosulfate on the rate of reaction (RP5)

Question 11

what can the direction of reversible reactions be changed by?

Answer 11

changing conditions

Question 12

what does dynamic mean

Answer 12

the forward and reverse reactions are both taking place at the same time

Question 13

what do the conditions have to be like for dynamic equilibrium to occur

Answer 13

the reaction has to be in a closed system

Question 14

in a closed system what is not possible to happen?

Answer 14

not possible for the products or reactants to escape the reaction vessel so there is no loss or gain in mass

Question 15

how do you push the reaction to the products (right)?

Answer 15

by adding heat

Question 16

how do you push the reaction to the reactants (left)?

Answer 16

by cooling it

Question 17

what can be observed when copper sulphate is being heated?

Answer 17

-blue solid becomes white solid
-some steam is released
-test tube cools as heat is absorbed to break copper bonds

Question 18

what can be observed when copper sulphate has been added water?

Answer 18

-white solid becomes blue solution
-test tube warms as heat is released due to formations of water bonds

Question 19

what does le chatelier’s principle state?

Answer 19

if the conditions of an equilibrium are changed the position of the equilibrium moves to the oppose the change and re-establish the equilibrium

Question 20

what does equilibrium mean?

Answer 20

at some point, the forward and the reverse reaction will take place at exactly the same rate

Question 21

what happens if you increase temp in dynamic equilibrium?

Answer 21

shift to endothermic route, more product

Question 22

what happens if you decrease temp in dynamic equilibrium?

Answer 22

shift exothermic, more reactant

Question 23

what happens if you increase pressure in dynamic equilibrium?

Answer 23

shift to fewer mol side, more product

Question 24

what happens if you increase pressure in dynamic equilibrium?

Answer 24

shift to higher mol, more reactant

Question 25

what happens if you increase concentration of reactants in dynamic equilibrium?

Answer 25

shift right, more product

Question 26

what happens if you increase concentration of product in dynamic equilibrium?

Answer 26

shift left, more reactant

Question 27

what is the formula to fins mean rate of reaction?

Answer 27

quantity of product formed / time taken

Question 28

on a graph for quantity of product formed what does it mean if the slope of the line is steep?

Answer 28

the steeper the slope, the faster the reaction

Question 29

on a graph for quantity of product formed, what does it mean if the line is flat and why?

Answer 29

the reaction has stopped, all of the reacting molecules have already reacted