Section 17.1

Reaction Rates and Equilibrium

1. Understand how particles in a mixture react with each other and the main factors that speed up or slow down a chemical reaction

2. Tell a homogeneous from a heterogeneous reaction by looking at the physical states of reactants and products

3. Recognize/define chemical equilibrium

Learning Goals – I will be able to…

Section 17.1

Reaction Rates and Equilibrium

A. How Chemical Reactions Occur

• Collision model – molecules must collide in order for a reaction to occur

Speeding up a reaction means having more collisions.How can we have more collisions between molecules?

Section 17.1

Reaction Rates and Equilibrium

Which solution is more concentrated?

A or B?

A or C?

B or C?

A B C

Which solution will have more collisions between molecules?

Section 17.1

Reaction Rates and Equilibrium

B. Conditions That Affect Reaction Rates

• Concentration – increases rate because more molecules lead to more collisions

• Temperature – increases rate – Why?

This is why a fever helps you fight disease – it increases the rate of metabolic reactions needed to make substances that

fight disease!

Effect of Surface Area on Reaction Rates

Ex.: HCl reacting with a piece of Mg

Section 17.1

Reaction Rates and Equilibrium

B. Conditions That Affect Reaction Rates

• Activation energy – minimum energy required for a reaction to occur

Section 17.1

Reaction Rates and Equilibrium

B. Conditions That Affect Reaction Rates

• Catalyst – a substance that speeds up a reaction without being consumed

– Enzyme – catalyst in a biological system

Section 17.1

Reaction Rates and Equilibrium

Flashback from Biology:How Enzymes Catalyze Metabolic Reactions

Section 17.1

Reaction Rates and Equilibrium

Section 17.1

Reaction Rates and Equilibrium

C. Homogeneous vs. Heterogeneous Reactions

• Homogeneous reaction – all reactants and products are in one phase – Gas – Solution

Section 17.1

Reaction Rates and Equilibrium

C. Homogeneous vs. Heterogeneous Reactions

• Heterogeneous reaction – reactants/products in two or more phases

Section 17.1

Reaction Rates and Equilibrium

C. Heterogeneous Reactions

Section 17.1

Reaction Rates and Equilibrium

D. The Equilibrium Condition

• Equilibrium – the exact balancing of two processes, one of which is the opposite of the other

Section 17.1

Reaction Rates and Equilibrium

D. The Equilibrium Condition

Section 17.1

Reaction Rates and Equilibrium

Chemical Equilibrium

• Chemical equilibrium – a dynamic state where the concentrations of all reactants and products remain constant

• Chemical reactions are reversible; the forward and reverse reactions eventually “cancel out” each other:

H2O + CO CO2 + H2

Section 17.1

Reaction Rates and Equilibrium

E. Chemical Equilibrium: A Dynamic Condition

Equal numbers of moles of H2O and CO are mixed in a closed container.

The reaction begins to occur, and some products (H2 and CO2) are formed.

The reaction continues as time passes and more reactants are changed to products.

Although time continues to pass, the numbers of reactant and product molecules are the same as in (c). No further changes are seen as time continues to pass. The system has reached equilibrium.

Section 17.1

Reaction Rates and Equilibrium

E. Chemical Equilibrium: A Dynamic Condition

• Why does equilibrium occur?

Section 17.1

Reaction Rates and Equilibrium

Check yourself for understanding:

• Answer the questions on your ch. 7 / 17.1 Review w.s.• Discuss your answers with a partner