Oxidation, Equilbria, Kinetics Flashcards
What is the Activation Energy?
The activation energy is the minimum amount of energy that particles require in order for a successful collision to occur
Rate Of Reaction
The rate of reaction is the change in the amount or concentration of a reactant or product over time.
What factors influence the rate of reaction?
The rate of reaction is influenced by many factors, including:
Temperature
Concentration
Pressure
Surface Area
Presence of Catalysts
How does Surface Area influence the rate of reaction?
- Increasing surface area of reactants increases the surface that is exposed to other particles and hence to possible collisions.
- The number of collisions that can take place at any one time increases.
- Therefore, increasing the surface area of a solid reactant increases the rate of the reaction.
Parts of the Maxwell Boltzman Distribution
Area under curve – the area under the curve is a measure of the total number of particles present.
Activation energy – A dotted line or straight line is used to represent the activation energy.
Shaded region – the shaded region to the right of the activation energy line represents the only particles that will react when they collide. These are the particles that have sufficient energy that is more than the activation energy.
Median (most common) particle energy – the peak of the curve represents the most common/likely energy of any single particle in the reaction.
Catalyst
A catalyst is a substance that increases the rate of a chemical reaction without being changed in chemical composition or amount.
Benefits of Catalyst usage
- lower production costs
- can improve properties of reaction products
- can reduce waste production because better atom economy
- more sustainable because allows for reactions to be done at lower temperatures and pressures
How does concentration influence rate of reaction?
- An increased concentration means more particles for a fixed volume.
- more particles closely packed together
- closer together so can collide more frequently
- Increase in no. of successful collisions.
How does pressure influence rate of reaction?
- An increased pressure means more particles for a fixed volume.
- more particles closely packed together
- closer together so can collide more frequently
- Increase in no. of successful collisions.
Collision Theory
- For a reaction to occur the particles involved must collide in the correct orientation with a sufficient energy.
How does temperature influence rate of reaction?
- An increase in temperature causes particles in a reaction to move faster as they gain more kinetic energy. The average speed of the particles increases.
- As the particles gain more kinetic energy, a greater proportion of these particles have energy more than the activation energy., so more can react.
- thus Increased in no. of successful collisions
What is a reversible reaction?
reaction that occurs in both directions
- The direction in which the reaction goes depends on its conditions.
Dynamic Equilibrium
- When the forward reaction is happening at the same RATE as the backward reaction
- At equilibrium the quantities/concentrations of reactants and products remain constant
- A dynamic equilibrium only occurs for a reversible reaction in a closed system
Le Chatelier’s Principle
If a dynamic equilibrium is disturbed by a change in conditions (temp,conc,F/A) then the position of equilibrium will shift to counteract the change.
This principle can be used to maximise percentage yields in industry.
Closed System
A system where nothing can be added or removed other than energy.
Haber Process
N2 + 3H2(G) <> 2NH3
conditions –> 400-450°C, 200atms
optimal conditions:
need to compromise conditions
to shift equilbirum - low temp, high atms
rate of reaction - high temp, high atm
financial cost - low temp, low atm
Effects of Temperature on Kc
- The value of Kc will change if the temperature is changed as the temperature change will affect the direction in which the reaction goes.
- An increase in Kc is dependent on an increase in product which will depend on what direction the reaction is in.
(same for decrease)
Effects of Concentration on Kc
Kc is unchanged.
Effects of a Catalyst on Kc
Kc is unchanged
- speeds up rate of reaction so equilibrium will be reached faster
Position of Kc
Kc = 1 <- same concentration of reactants and products
Kc > 1 <- position of equilibrium is shifted to the right
Kc < 1 <- position of equilibrium is shifted to the left
finding Kc with homogeneous & heterogeneous reactions
- Equilibrium constant only works for homogeneous reactions (all products and reactants are in the same phase)
however:
S + L <- can calculate Kc but must ignore solid
S+ G <- can calculate Kc but must ignore solid
L + G <- cannot calculate kc but can find Kp
What happens to the amount of product formed when there is an increase in concentration of reactants in a reversible reaction?
- increased reactants
- equilibrium shifts to the left
- thus more product formed from excess reactant
(opposite for if concentration decreases)
What happens to the amount of reactant formed when there is an increase in concentration of products in a reversible reaction?
- increased product
- equilibrium shifts to the right
- thus more reactant formed from excess product
(opposite for if concentration decreases)
What happens to the reactants and products of a reversible reaction when the pressure is increased?
- increased pressure
- equilibrium will shift to side of fewest moles
- equilibrium will be restored due to lower pressure again by shifting to the side of fewest moles
What happens to the reactants and products of a reversible reaction when the pressure is decreased?
- decreased pressure
- equilibrium will shift to side of greatest moles
- equilibrium will be restored due to greater pressure again by shifting to the side of the greatest moles
What happens to a dynamic equilibrium when temperature is increased?
- shifts to the endothermic direction
- endothermic reactions requires heat so will remove excess heat from the system
What happens to a dynamic equilibrium when temperature is decreased?
- shifts to the exothermic direction
- exothermic reactions release heat so will add extra heat to the system to restore balance.
What is disproportionation?
When an element in a single species in a chemical reaction is simultaneously being oxidised and reduced.
e.g chlorine
Cl2 + 2NaOH –> NaCl(aq) + NaClO + H2O
0 -1 +1
what is a redox process?
When both reduction and oxidation happen simultaneously.
When are Oxygen, Hydrogen and Chlorine’s oxidation numbers different?
Oxygen is -1 for peroxides, Hydrogen is different for metal hydrides, and chlorine when bonded with fluorine and oxygen.
