The Rate and Extent of Chemical Change

Rate of Reaction

The speed at which reactants are turned into products.

Collision Theory

A reaction happens when particles collide with enough energy.

Activation Energy

The minimum energy required for particles to react.

Catalyst

A substance that speeds up a reaction without being used up.

Reversible Reaction

A reaction that can go in both directions (forward and backward).

Dynamic Equilibrium

The point in a closed system where forward and reverse reactions occur at the same rate.

Le Chatelier’s Principle

If a system at equilibrium is changed, it will shift to oppose the change.

How do you calculate rate of reaction?

Rate = Amount of reactant used or product formed ÷ Time

What are the main factors that affect rate?

• Temperature

• Concentration or pressure

• Surface area

• Catalysts

How does increasing temperature affect rate?

Particles move faster → more frequent and more energetic collisions → higher rate.

Why do powders react faster than lumps?

Powders have a larger surface area, so more collisions per second.

What makes a collision "successful"?

The particles collide with enough energy (≥ activation energy).

How do catalysts work?

They provide an alternative reaction pathway with a lower activation energy.

Biological catalysts = enzymes (in living systems).

Industrial example: Iron catalyst in the Haber Process.

Magnesium + Hydrochloric Acid practical

Measures rate by volume of hydrogen gas produced.
Equation:

Sodium Thiosulfate + Hydrochloric Acid

Produces sulfur = cloudy solution. Measure time for cross to disappear.
Investigates effect of temperature or concentration on rate.

• Steeper slope = faster rate

• Flat line = reaction has finished

Calculate rate from graph:

• Use tangent for rate at a point

• Use gradient = rise/run

Reversible Reactions

Products can react to form reactants again.

Forward reaction and Backward reaction

Exothermic and Endothermic