5.1.2 How Far: Module 5: Physical Chemistry & Transition Elements: Chemistry OCR A A Level

What does it mean when a reaction is at equilibrium?

The rate of forward and reverse reactions are equal.

What are the methods that can be used to measure equilibrium?

● Measure change in colour or colour intensity using colorimeter.

● Use pH probe.

● Measure electrical conductivity.

● Titration - used when equilibrium is slow so that titration can be completed before there is much change in equilibrium mixture.

What does mole fraction mean?

The amount of a given component in a given reaction mixture.

Write the equation used to calculate mole fraction.

Mole fraction = number of moles of substance A / total number of moles of all substances

What does partial pressure mean?

The pressure exerted by a single species in a reaction vessel.

What is the symbol for partial pressure?

P

Write the equation used to calculate partial pressure.

Partial pressure = Mole fraction x total pressure

What is the relationship between concentration of a substance and its partial pressure?

Concentration of a substance is proportional to its partial pressure.

What are the 3 common units of pressure used in chemistry?

● Pascals

● Atmospheres

● Newtons per square metre

What type of brackets are used in Kc expressions?

Square Brackets

What type of brackets are used in Kp expressions?

Round Brackets

How do you calculate the units for Kp?

Write out the units for the partial pressures in the same arrangement as the Kp equation and cancel out/multiply together. Usually in Pa, kPa, atm etc. DO NOT CHANGE UNITS.

What is the symbol of equilibrium constant?

K

What does it mean when K is greater than 1?

Reaction favours product.

What does it mean when K is lesser than 1?

The reaction favours reactants.

What is the effect of increasing temperature on K?

Equilibrium shifts to the direction of endothermic reaction.

What is the effect of decreasing temperature on K?

Equilibrium shifts to the direction of exothermic reaction.

What is the only factor that affects K?

Temperature

What is the effect of increasing temperature on K for a forward endothermic reaction?

K increases as temperature increases.

What is the effect of increasing temperature on K for a forward exothermic reaction?

K decreases as temperature increases.

What effect does catalyst have on K ?

Catalysts does not affect the position of equilibrium, they only have an effect on the rate of reaction.