C5

How to calculate Percentage yield

How to calculate Percentage yield

Percentage yield = actual yield/theoretical yield x100

Why is percentage yield always less than 100%?

Reaction may not have completed
Unwanted side reactions take place
Some products lost in isolation such as during filtration
Reactants could be impure
Reaction may be reversible

How to calculate atom economy

Atom economy = Mr of desired product/ Total Mr of all products x100

Include number at the front

Dm³ to Cm³ conversions

1 Dm³ = 1000 cm³
1 dm³ = 1L
1 cm³ = 1ml

How to calculate concentration in mol/dm³

Concentration = Moles/volume
Volume = moles/concentration
Moles = Concentration x volume

How to calculate concentration in g/dm³

Conc. g/dm³ = Conc. mol/dm³ x Mr

Describe titration practical

Place acid in the biurette and measure initial volume
Measure fixed volume of alkali using a pipette and place it in a conical flask and add indicator
Add acid from burette slowly and swirl until there is a colour change (place conical flask over a white tile)
Measure fixed volume of acid in burette
Calculate titre by doing final - initial volume
Repeat until you get concordant results
Calculate mean

How to calculate volume of gas

Volume of gas = moles x 24dm³
Moles = volume of gas/24dm³

How does a reaction occur (Collision theory)

Particles have to collide with a certain amount of energy (activation energy)

What factors does rate of reaction depend on?

Frequency of collision between particles
Orientation in which particles collide
Energy with which particles collide

How to calculate Rate of reaction

Rate over a period of time (Initial rate)- Calculate gradient of the line (usually straight)
Rate at particular point- Draw a tangent at the point and calculate gradient of the tangent

How does temperature affect reaction rate?

Higher temperature, faster rate of reaction
Particles have more kinetic energy and move faster, more collisions per second
More frequent successful collisions as more collisions per second and more have activation energy

How does concentration affect reaction rate?

Higher conc. more particles in same amount of volume
Particles become more crowded so more likely to collide successfully
More frequent collisions

How does surface area affect reaction rate?

Smaller particle size of solid reactant (SA), faster rate of reaction
As SA increases, more contact area for (non-solid) reactant particles to collide with.

Define catalyst and some examples of everyday catalysts

Catalyst- substances that increase reaction rate without being used up in reaction. Never produce more product. Amy Transition metals or their compounds

Nickel- catalyst for production of margarine (hydrogenation of vegetable oils)
Iron- Catalyst in production of ammonia from nitrogen and hydrogen
Platinum- catalyst in catalytic converters of car exhausts. Catalyses conversion of carbon monoxide and nitrogen oxide into less pollution CO2 and nitrogen

Name a biological catalyst and what it does

Enzymes help in reactions of the body by controlling reaction rate eg. yeast an enzyme used in fermentation.
Alcohol can be used in making drinks and CO2 can make bread rise.
Enzymes denature beyond 40C and different pH levels

Define Equilibrium

Equilibrium- reversible reaction in closed system. Rate of forward and backward reaction the same. Amount/concentration of products and reactants remain constant

Describe an equilibrium graph

Reactant conc. start high and decrease as reaction proceeds. Forward rate decreases
Product conc. start at 0 and increases as reaction proceeds. Reverse rate also increase
Eventually forward rate and reverse rate and conc. are all constant

How does EQ position differ

EQ position on left when conc. of reactant > conc. of products
EQ position on right when conc. of reactant < conc. of products

What is Le Chatelier’s principle

When a system in dynamic equilibrium undergoes change, position of EQ fights back to minimise change

How does concentration affect EQ position

Conc. of reactant increases, EQ position to the right
Conc. of product increases, EQ position to the left

How does pressure affect EQ position

Increasing pressure shifts EQ position to side with fewer gas molecules (vice versa)
Ignore any solids or liquids in equation

How does Temperature affect EQ position

Increase temp, EQ position towards endothermic direction
Decrease temp, EQ position towards Exothermic direction