topic six: rate and extent of chemical change

Question 1

give the equations regarding mean rate of reaction

Answer 1

mean rate of reaction = quantity of reactant used / time
mean rate of reaction = quantity of product formed / time

Question 2

what can the quantity of a chemical be measured in?

Answer 2

mass in grams / volume of gas in cm3 / amount in moles

Question 3

why do we draw reaction rate graphs?

Answer 3

they can be drawn to show how the quantity of reactant used or product formed changes with time

Question 4

what does the slope represent in a reaction rate graph?

Answer 4

the rate of reaction thus the steeper the slope, the faster the reaction

Question 5

how would we find the rate of reaction at a single point?

Answer 5

by drawing a tangent to the curve and calculating the slope

Question 6

what is the formula for calculating the slope?

Answer 6

change in y / change in x

Question 7

define activation energy

Answer 7

the minimum amount of energy particles need to react

Question 8

when do successful collision occur?

Answer 8

when reactant particles collide with enough energy to react

Question 9

what does the rate of a reaction depend on? (regarding collision theory)

Answer 9

the frequency of successful collisions

Question 10

how does temperature influence the rate of a reaction?

Answer 10

the higher the temperature, the faster the reaction. this is because the particles have more energy so they have enough energy to react when the collide

Question 11

how does concentration influence the rate of a reaction?

Answer 11

the higher the concentration, the more particles of a solute that are dissolved. the higher the concentration of reactant in solution, the greater the rate of reaction. this is because there are more reactant particles in the solution meaning a successful collision is more likely to occur.

Question 12

how does the pressure of reacting gases influence the rate of a reaction?

Answer 12

the greater the pressure of a gas, the closer the reactant particles are together so the higher the pressure the faster the reaction. this is because the reactant particles are closer together so there are more frequent successful collisions.

Question 13

how does surface area of solid reactant influence the rate of a reaction?

Answer 13

when a solid is in powder form, it has a greater surface area. the greater the surface area, the faster the rate of reaction. this is because there are more particles on the surface that can react so there are more frequent successful collisions.

Question 14

how does the presence of a catalyst influence the rate of a reaction?

Answer 14

when a catalyst is present, the activation energy is lowered meaning the particles require less energy to react and thus do so more frequently.

Question 15

define a catalyst

Answer 15

a substance that speeds up a chemical reaction without getting used up in the process

Question 16

give an example of a biological catalyst

Answer 16

an enzyme e.g. amylase or protease

Question 17

draw the graph showing the effect of temperature on the rate of a reaction

Answer 17

rate of reaction on the y-axis
temperature on the x-axis
a curved slope meaning it is NOT proportional

Question 18

draw the graph showing the effect of the concentration of a solution on the rate of a reaction

Answer 18

rate of reaction on the y-axis
concentration of a solution on the x-axis
a straight line from the origin indicating that they are directly proportional (as one increases so does the other)

Question 19

draw the graph showing the effect of gas pressure on the rate of a reaction

Answer 19

rate of reaction on the y-axis
gas pressure on the x-axis
a straight line from the origin indicating that they are directly proportional (as one increases so does the other)

Question 20

draw the graph showing the effect of surface are of solid reactants on the rate of a reaction

Answer 20

rate of reaction on the y-axis
surface are of solid reactants on the x-axis
a straight line from the origin indicating that they are directly proportional (as one increases so does the other)

Question 21

define reversible reaction

Answer 21

once the products of the reaction have been made from the reactants, the products can react again to form the reactants

Question 22

what is the forward and backward reaction in a reversible reaction

Answer 22

the forward reaction is when the reactants form the products and the backward reaction is when the products form the reactants

Question 23

discuss the type of reactions in a reversible reaction

Answer 23

if the forward reaction is exothermic then the backward reaction will be endothermic and vice versa e.g. forward reaction: -82kJ then backward reaction: 82kJ

Question 24

define a dynamic equilibrium

Answer 24

both the forward and backward reactions are taking place simultaneously and at exactly the same rate of reaction

Question 25

what are the conditions required for a dynamic equilibrium?

Answer 25

the reversible reaction must take place in a closed system where no substances can get in or out

Question 26

define what it means when an equilibrium lies to the left

Answer 26

it means there are more reactants than products in the mixture of chemicals at equilibrium

Question 27

define what it means when an equilibrium lies somewhere in the middle

Answer 27

it means there is a similar amount of products and reactants in the mixture of chemical at equilibrium

Question 28

define what it means when an equilibrium lies to the right

Answer 28

it means there are more products than reactants in the mixture of chemicals at equilibrium

Question 29

what does le châtelier’s principle state?

Answer 29

if a change is made to the conditions of a system at equilibrium then the position of the equilibrium moves top oppose that change in conditions

Question 30

discuss the effect of changing the concentration of a reactant on the position of the equilibrium

Answer 30

increasing the concentration means that the equilibrium will shift to the right to reduce the concentration
decreasing the concentration means that the equilibrium will shift to the left to increase the concentration

Question 31

discuss the effect of changing the concentration of a product on the position of the equilibrium

Answer 31

increasing the concentration means that the equilibrium will shift to the left to reduce the concentration
decreasing the concentration means that the equilibrium will shift to the right to increase the concentration

Question 32

discuss the effect of changing the temperature on the position of the equilibrium in a reaction where the forward reaction is exothermic

Answer 32

increasing the temperature means that the equilibrium will shift to the left (the endothermic direction) to lower the temperature
decreasing the temperature will move the equilibrium to the right (the exothermic direction) to increase the temperature

Question 33

discuss the effect of changing the temperature on the position of the equilibrium in a reaction where the forward reaction is endothermic

Answer 33

increasing the temperature means that the equilibrium will shift to the right (the endothermic direction) to lower the temperature
decreasing the temperature will move the equilibrium to the left (the exothermic direction) to increase the temperature

Question 34

discuss the effects of pressure on the position of the equilibrium when there are more reactant gas molecules than product ones
e.g. 2A(g) <—> B(g)

Answer 34

increasing the pressure will move the equilibrium to the right, the side with less gas molecules to reduce pressure
decreasing the pressure will more the equilibrium to the left, the side with more gas molecules to increase pressure

Question 35

discuss the effects of pressure on the position of the equilibrium when there are more product gas molecules than reactant ones
e.g. A(g) <—> 2B(g)

Answer 35

increasing the pressure will move the equilibrium to the left, the side with less gas molecules to reduce pressure
decreasing the pressure will more the equilibrium to the right, the side with more gas molecules to increase pressure

Question 36

do catalysts have an effect on the position of the equilibrium

Answer 36

it has no effect however it does increase the rate of forward and backward reactions, both by the same amount. this means that the system reaches equilibrium faster