Chem - Topic 6

Rate of Reaction

Measure of how fast reactants are used up

Collision Theory

Particles must collide with enough energy to overcome the activation energy.

What does a rate of reaction depend on 

The collision frequency of reacting particles. The more collisions there are the faster the reaction

The energu transferred during a collision, Particles must collide with enough energy.

Activation Energy

Minimum energy needed for reaction to occur

graphs and tangents and shii

How does increasing temperature increase the rate?

• Particles move faster

• So more frequent collisions, so increases the rate of reaction.

• In addition, when particles move faster, the more energy they have. So more of the particles will have enough energy for reaction to occur.

How does increasing concentration increase the rate?

More particles in the same volume, (same with pressure).

So more frequent collisions.

How does increasing surface area increase the rate?

Breaking a solid into smaller pieces, increase the SA:V ratio.

So particles have more area to work, so more frequent collisions

How does increasing catalyst increase the rate?

Provides an alternative reaction pathway, to decrease the activation energy

So more particles have enough energy to react.

Reversible Reaction

A chemical reaction where products can react to re-form original reactants.

What happens to energy changes in reversible reactions?

In reversible reactions:
If the forward reaction is exothermic, the reverse is endothermic.
If the forward is endothermic, the reverse is exothermic.

Equilibrium

Equilibrium is reached when the rate of forward reaction equals the rate of backward reaction.

What are the conditions eeeded for Equilibrium

Equilibrium is only established in a closed system → no reactants or products can escape.

Le Chatelier’s Principle

If a system at equilibrium is disturbed, it shifts to oppose the change and restore a new equilibrium.

Effect of Temperature

• Increase temp → shifts to endothermic direction
• Decrease temp → shifts to exothermic direction

Effect of Pressure

• Increase pressure → shifts to side with fewer gas molecules
• Decrease pressure → shifts to side with more gas molecules

Effect of Concentration

• Increase reactant → shifts right (makes more products)
• Remove product → shifts right
• Increase product → shifts left (forms more reactants)