Topic 6: the rate and extent of chemical change

Question 1

two calculations for how rate of reaction is calculated

Answer 1

rate of reaction = amount of reactant used or product formed / time

or

rate of reaction = moles of reactant used or product form / time

Question 2

3 most common ways of measuring rate of reaction

Answer 2

loss in mass or reactants
volume of gas produced
time for a solution to become opaque

Question 3

describing measuring the rate by monitoring mass loss

Answer 3

place the reaction flask on a balance.
in these reactions, a gas is given off - so record the decrease is mass in timed intervals
plot a graph

Question 4

describe measuring the rate by monitoring the volume of a gas

Answer 4

connect a gas syringe to a reaction flask and measure the volume of a gas formed in time intervals
plot a graph of volume vs time

Question 5

describe measure the rate by monitoring the disappearance of a cross

Answer 5

take a piece of paper and mark a cross
put the reaction flask on the cross
mix the reagents and measure how long it takes for a cloudy mixture to conceal the cross (turn cloudy and you cannot see it)

Question 6

how to find a rate of reaction at some time from a graph of around of reactant vs time

Answer 6

pick a point corresponding to the time and find the tangent to the curve at a point
the tangent is the gradient of this graph, it tells you how fast the reaction proceeds at this point. the steeper the tangent lines, the faster the rate

Question 7

5 factors effecting the rate of chemical change

Answer 7

concentration of reactants
pressure of gases
surface area
temperature
catalysts

Question 8

what is the collision theory

Answer 8

chemical reactions can occur only when reacting particles collide with each other with sufficient energy

Question 9

describe the effect of increasing temp on the rate of reaction

Answer 9

temp increase = faster reaction
as temp increases, kinetic energy of particles increase, so they move faster also equalling more collisions

Question 10

describe the effect of increasing concentration on the rate of reactions

Answer 10

concentration increases = faster reaction
more reactants then equal more frequent collisions

Question 11

describe the effect of increasing pressure of a gas on the rate of reaction

Answer 11

increasing the pressure of reacting gases, is the same as increasing concentration. it increases the number of gas molecules in the same volume and so increases the frequency of collisions and therefore increases the rate of reactions

Question 12

describe the effect of increasing surface area on reactions

Answer 12

if solid reactants are in similar pieces, they have a greater surface area
increasing the surface area of solid reactants increases the frequency of collisions and so increases the rate of reactions

Question 13

what is a catalyst

Answer 13

a catalyst changes the rate of reaction but it is not used up
increases the rate of reaction by providing a different pathway for the reaction that has a lower activation energy. the reaction profile for a catalyst reaction will have a lower maximum of the curve

Question 14

what is an enzyme

Answer 14

an enzyme is a molecule that acts as a catalyst is a biological system

Question 15

what is a reversible reaction

Answer 15

a reversible reaction occurs when the products of a reaction can react backwards to produce the original reactions

Question 16

when is dynamic equilibrium reached

Answer 16

in a closed system
when the forward and reverse reactions occur at the same rate and the concentrations of reactants and products remain constant

Question 17

describe le chapeliers principle

Answer 17

if a system is at equilibrium and a change is made to any of the conditions, then the system responds to counteracts change and restore equilibrium

Question 18

describe the effect of changing the concentration of the reactant and product on the position of the equilibrium

Answer 18

if the concentration of one of the reactants or products is changed, the system is no longer at equilibrium and the concentrations of all the substances will change until equilibrium is reached again. in the concentration of a reactant is increases, more products will be formed until equilibrium is reached again. if the concentration of a product is decreased, more reactants will react until equilibrium is reached again

Question 18

describe the effect of changing temp on the position of the equilibrium

Answer 18

in the temp of a system at equilibrium is increases:

• the relative amount of products at equilibrium increases for an endothermic reaction
• the relative amount of products of equilibrium decreases for an exothermic reaction

Question 19

describe the effect of changing pressure on the position of the equilibrium

Answer 19

an increase in pressure will cause the equilibrium position to shift towards the side with the smaller number of molecules as shown by the symbol equation for that reaction.

a decrease in pressure causes the equilibrium position to shift towards the side with the larger number of molecules as shown by the symbol equation for that reaction.

pressure has no effect on the reactions where the numbers of gas molecules are equal on both sides on the equation

Question 20

describe the effect of the catalyst on the position of the equilibrium

Answer 20

no effect
speeds up both forward and backward reactions equally