IB SL Chemistry - Reactivity 2

Limiting Reactant

The reactant used up completely in the reaction, while other reactants are present in excess (more than required by the mole ratio). Note: Controls the theoretical yield of the reaction.

Law of Conservation of Mass

The total mass of the products in the reaction is equal to the total mass of the consumed reactants.

Equation for percentage yield

(experimental value) / (theoretical value) x 100, note: values can be in moles or mass.

True or False: Theoretical yield is smaller than or equal to the experimental yield.

False- Theoretical yield is greater than or equal to the experimental yield.

Green chemistry and examples

Takes into account the environmental impacts of the entire technological process. Examples: Aqueous or solvent-free reactions, renewable starting materials, mild reaction conditions, efficient catalysts, etc.

What is atom economy and its equation?

Atom economy if the measure of efficiency of a reaction: (molar mass of desired product) / (total mass of reaction mixture) x 100

Equation for the (average) rate of reaction

v=|Δc| / Δt = (change in concentration) / (per unit of time)

Instantaneous reaction rate

v_insta= |dc| / dt, note: this is the derivative and you are looking for the slope of that tangent.

What three things are necessary for a chemical reaction to occur?

1) Two (or more) particles must collide with each other.

2) The colliding particles must have the correct mutual orientation.

3) The sum of the kinetic energies of the particles must be sufficient to initiate the reaction.

Activation energy, E_a

The minimum amount of kinetic energy, E_k, required to start the reaction.

How to calculate reaction enthalpy, ΔH_r

Initial energy level (reactants) - final energy levels (products)

Catalyst

A substance that increases the rate of a chemical reaction (by lowering the activation energy level) and is not consumed in the reaction.

Describe what an intermediate is in a reaction with a catalyst

When a catalyst reacts with a reactant to form an unstable compound, that is an intermediate. The product is stable but can only exist for a short period of time.

The intermediate undergoes further chemical changes and eventually forms the reaction product, releasing the catalyst.

Describe what a transition state is in a reaction with a catalyst

A particular configuration of atoms along the reaction pathway that has a short life at the high-energy point of the reaction.

How are biochemical reactions catalysed?

By proteins called enzymes.

Describe how concentration affects reaction rates

An increase in concentration leads to more frequent collisions between particles, so the reaction rate increases.

Describe how pressure affects reaction rates

An increase in pressure leads to more frequent collisions between particles, so the reaction rate increases. Pressure only affects gaseous reactants.

Describe how surface area affects reaction rates

An increase in surface area leads to more frequent collisions between phases, so the reaction rate increases.

Heterogeneous mixture

A mixture where the composition is not uniform throughout.

Phase

An individual substance or mixture that has uniform chemical and physical properties.H

Homogeneous mixture

A type of mixture where the components are evenly distributed with the same composition throughout.

Describe how temperature affects reaction rates

When temperature increases, the average speed and kinetic energy of particles also increases. The particles move faster, they collide with each other more often, so there is a higher percentage of successful collisions.

Dynamic equilibrium

Where the rates of the forward and reverse reactions are equal. AKA the chemical equilibrium.

True or False: The dynamic equilibrium can only be reached if the reversible reaction happens in a close system.

True

True or False: When reaching dynamic equilibrium, changes only occur at the macroscopic level, not the microscopic level.

False

Heterogeneous Equilibrium

Where the two participating species are present in different species. Sat

Saturated solution

The highest possible concentration of the solute under given conditions. Un

Unsaturated solution

Contains less solute than possible, so that it can dissolve an additional quantity of that solute.

Equilibrium Law (in regards to K)

When a chemical system is at equilibrium and temperature is constant, K = ([x]^x[Y]^y) / ([A]^a[B]^b), where x and y are products and a and b are reactants.

What does the k value mean?

The direction and extent of the spontaneous process under STP

Which direction is the reaction favored when K > 1? K < 1? K = 1?

If K > 1, products are favored. If K < 1, reactants are favored.

If K = 1, the equilibrium will have about equal concentrations of reactants and products.

What happens to the K value when all the coefficients are halved?

K’ = √K

What happens to the K value when all the coefficients are doubles?

K’ = K²

What happens to the K value when all the coefficients are halved?

What happens to the K value when the equation is reversed?

K’ = 1/K

What happens to the K value when two equations are added together?

K’ = K₁ x K₂

Le Chatelier’s Principles

When the dynamic equilibrium is affected by a change in reaction conditions, the processes will shift to counteract the change and return to equilibrium.

What happens when the equilibrium of the reaction shifts right?

The forward reaction become more favorable + the concentration of products increases.

What happens when the equilibrium of the reaction shifts left?

The reverse reaction become more favorable + the concentration of reactants increases.