chem chp 8 9 definitions

Dynamic Equilibrium

State in which the forward and backward reactions occur at equal rates in a closed system, so concentrations remain constant.

Reversible Reaction

A reaction that can proceed in both forward and backward directions.

Closed System

A system in which no substances enter or leave.

Le Chatelier’s Principle

When a system at equilibrium is disturbed, the equilibrium shifts to oppose the change.

Equilibrium Position

The relative amounts of reactants and products present at equilibrium.

Equilibrium Constant (Kc)

A constant showing the ratio of product concentrations to reactant concentrations at equilibrium.

Kp

An equilibrium constant expressed using partial pressures of gases.

Partial Pressure

The pressure exerted by one gas in a mixture of gases.

Concentration

The amount of substance dissolved per unit volume.

Exothermic Reaction

A reaction that releases heat energy to the surroundings.

Endothermic Reaction

A reaction that absorbs heat energy from the surroundings.

Catalyst

A substance that increases the rate of reaction without being chemically changed.

What changes Kc and Kp?

Only temperature changes Kc and Kp.

Do catalysts change equilibrium position?

No, catalysts only help equilibrium be reached faster.

Which substances are included in Kc and Kp expressions?

Only gases (g) and aqueous substances (aq).

Which substances are excluded from Kc and Kp expressions?

Solids (s) and liquids (l).

Rate of Reaction

The change in concentration or amount of reactant/product per unit time.

Collision Theory

Chemical reactions occur when particles collide with sufficient energy and correct orientation.

Successful Collision

A collision with enough energy to cause a reaction.

Activation Energy

The minimum energy particles must have for a successful collision.

How does a catalyst increase rate?

By providing an alternative reaction pathway with lower activation energy.

Gradient

The change in y divided by the change in x on a graph.

Formula for gradient

Gradient = change in y ÷ change in x

Tangent

A straight line touching a curve at one point used to find instantaneous rate.

Instantaneous Rate

The rate of reaction at one specific moment in time.

Initial Rate

The rate of reaction at the start of the reaction.

Frequency of Collision

The number of collisions occurring per second.

Effect of increasing temperature on rate

Particles gain more kinetic energy and more successful collisions occur.

Effect of increasing concentration on rate

Particles collide more frequently, increasing rate.

Effect of increasing pressure on gases

Gas particles are closer together, causing more frequent collisions.

Effect of increasing surface area

More particles are exposed for collisions, increasing rate.

What does a steep graph mean?

A fast reaction rate.

What does a shallow graph mean?

A slow reaction rate.

Why does a reaction graph flatten?

Reactants are used up so the rate decreases.

Formula for rate of reaction

Rate = change in quantity ÷ time taken

What does equilibrium mean?

The forward and backward reaction rates are equal.

What happens if a reactant is added at equilibrium?

Equilibrium shifts right to use up the added reactant.

What happens if a product is removed at equilibrium?

Equilibrium shifts right to replace the removed product.

Effect of increasing pressure on equilibrium

Equilibrium shifts to the side with fewer gas molecules.

Effect of decreasing pressure on equilibrium

Equilibrium shifts to the side with more gas molecules.

Effect of increasing temperature on exothermic reactions

Equilibrium shifts left.

Effect of increasing temperature on endothermic reactions

Equilibrium shifts right.

What happens when a catalyst is added to an equilibrium?

Equilibrium position does not change.

Rule for writing Kc and Kp expressions

Products over reactants.

What happens to coefficients in equilibrium expressions?

They become powers.