Chemistry Study Guide Test 11

Rates of reactions can be determined by monitoring the change in…

CONCENTRATION of reactants or products and a change in time. ( Δ[ ]/ ΔTime)

The average rate of the reaction over each interval is..

• the change in concentration divided by the change in time

• ↓Concentration = ↓Rate of reaction

• Less collisions = less of reaction

Collision Theory/Model

• Molecules CANNOT react unless they “bump” into each other

• Not all collisions are effective

• Collisions must have sufficient energy and proper orientation to collide

Activation energy

minimum amount of energy required for a reaction to occur

A reaction cannot occur UNLESS…

molecules possess enough energy to prevail the activation energy border

Reaction Coordinate Diagram 

• An activated complex is intermediate product of the reaction

• Activation energy goes over the energy barrier

• ΔH is depicted between the reactant and products 

• +ΔH is endo, -ΔH is exo, EXOTHERMIC REACTION NEEDS LESS ACTIVATION ENERGY

Factors of Reaction Rate

• ⭡Reaction rate = ⭡effective collisions

• ⭡amount of reactants

• ⭡surface area

• Stirring

• Adding a catalyst

• ⭡Temperature (more kinetic energy, particles move faster)

Opposite of catalyst

inhibitors

• Homogeneous catalysts: same state of matter

• Heterogeneous catalysts: different state of matter

Equilibrium

reversible processes, rate of the forward reaction=rate of reverse reaction

Equilibrium Phase Diagram

• Reactants begin to decrease when products begin to increase (get used up)

• Opposite of forward reaction

• Equilibrium reached when lines flatten out

At equilibrium: Rate of forward reaction = rate of reverse reaction, concentration of reactants and products is CONSTANT

Equilibrium in chemistry: balance of opposite processes (movement)

Equilibrium equation

K = equilibrium constant: K = [concentration of products]/[concentration of reactants]

• Solids and pure liquids are NOT included

• Coefficients become exponents

• Nothing BUT TEMPERATURE changes equilibrium constant

Le Chatelier’s Principle

An equilibrium system subjected to a stress will shift to counteract it.

• Types of stresses: change in temperature, change in concentration, change in volume or pressure (for gases)

• Catalyst is NOT a stressor

Law of Mass of Action

• ratio of concentration products/ratio of concentration reactants = constant

Haber Process

N2 + 3H2 ↔ 2NH3

• If H2 is added, N2 will be consumed and the reagents will form MORE NH3

• Pressure is proportional ONLY to moles of gas in the system

Mass Action Expression

• Q: any point in reaction (reaction quotient)

• K: @ equilibrium (equilibrium constant)

Q vs. K

Q>K: equilibrium shifts to reactants

Q≅K: equilibrium

Q<K: equilibrium shifts to products