6. The Rate and Extent of Chemical Change

What is the equation for rate of reaction using reactants?

Rate = amount of reactant used ÷ time

What is the equation for rate of reaction using products?

Rate = amount of product formed ÷ time

What are the possible units for rate of reaction?

g/s, cm³/s, mol/s (depending on quantities measured)

How can the mass of reactants be measured during a reaction?

Using a balance to record change in mass over time

How can the volume of gas be measured during a reaction?

Using a gas syringe or inverted measuring cylinder in water

Name five factors that affect the rate of a chemical reaction.

Concentration of solutions, pressure of gases, surface area of solids, temperature, catalysts

Why does increasing concentration increase the rate of reaction?

More particles in the same volume = more frequent collisions

Why does increasing pressure increase the rate of reaction?

Particles are closer together = more frequent collisions

Why does increasing surface area increase the rate of reaction?

More particles exposed = more frequent collisions

Why does increasing temperature increase the rate of reaction?

Particles have more kinetic energy = more frequent and more energetic collisions

What is the role of a catalyst?

To increase the rate by lowering activation energy without being used up

What does collision theory state?

Particles must collide with enough energy (activation energy) for a reaction to occur

In reversible reactions, if the forward reaction is exothermic, what is the reverse reaction?

Endothermic

In reversible reactions, how much energy is transferred in each direction?

The same amount

Give an example of a reversible reaction.

Ammonium chloride ⇌ ammonia + hydrogen chloride

What is a closed system?

A system where no reactants or products can enter or leave

What is equilibrium?

The point in a reversible reaction where the rate of the forward and reverse reactions are equal and concentrations remain constant

State Le Chatelier’s Principle.

If conditions are changed, the system shifts to counteract the change

If the concentration of a reactant is increased, which way does equilibrium shift?

To the products

If the concentration of a product is increased, which way does equilibrium shift?

To the reactants

If temperature is increased, which direction is favoured?

The endothermic direction

If temperature is decreased, which direction is favoured?

The exothermic direction

If pressure is increased, which side is favoured?

The side with fewer gas molecules

If pressure is decreased, which side is favoured?

The side with more gas molecules

Which industrial process uses equilibrium principles?

The Haber process