10- Reaction Rates And Equilibrium Flashcards
Rate of a chemical reaction definition
Measures how fast the reactants are being used up or products are being formed
Rate of reaction (concentration) definition
The change in concentration of a reactant or product in a given time
What conditions are required for a reaction to take place
The particles collide with the correct orientation
The particles must have sufficient energy to overcome the activation energy barrier of the reaction
Activation energy definition
The minimum amount of kinetic energy required for a reaction to occur
What 5 things can alter the rate of a chemical equation
Increasing temperature
Increasing SA
Increasing pressure
Increasing concentration
Use of a catalyst
How does temperature affect the rate of reaction
Temperature increases the rate of reaction by…
Increases KE of particles
Greater proportion of the particles will have at least the activation energy - more effective collisions
Causes them to move faster and collide more frequently increasing the chances of effective collisions
How does concentration / pressure alter rate of a chemical reaction
Increasing concentration/pressure increases the rate of reaction
It increases the number of particles in the same volume
Particles are closer together
Collide more frequently
More likely to be more effective collisions
How do catalysts affect rate of reaction
Catalysts increase rate of reaction
They lower the activation energy
By providing an alternative reaction pathway
A greater proportion of particles will have enough energy to react
What are the different types of ways to measure reaction rates
How quickly the reactants are used up = removal of reactant
How quickly the products are formed = formation of a product
List of ways of measure rate of reaction practicals
Record then graph …
- colour changes in solutions
- mass change
- volume of gas produced
- pressure changes in gasses
- changes in conductivity
Monitoring the loss of mass of reactants using a balance practical
1) add reactants to conical flask
2) record initial mass
3) add catalyst
4) record mass at regular intervals until no change
Monitoring volume of gas produced at regular time intervals using gas collection
1) add reactants to conical flask and replace bung
2) record the initial volume
3) add catalyst
4) measure volume at regular interval changes
Catalyst definition
A catalyst increases the rate of reaction by providing an alternative reaction pathway with a lower activation energy. The catalyst is chemically unchanged by the end of the reaction
Heterogeneous catalyst definition
A reaction in which the catalyst has a different physical state from the reactants
Reactants = gases Catalyst = solid
How does a heterogenous catalyst operate
Reaction takes place on surface of the catalyst
Reactant is absorbed onto surface (forms weak bonds)
Product leaves through desorption
Homogenous catalyst definition
A reaction in which the catalyst and the reactants are in the same physical state
Aqueous
How do homogeneous catalysts operate
Catalysts react with the reactants to form an intermediate species
Which breaks down to give products and regenerates the catalyst
What is the economic importance of catalysts
- Catalysts lower the production costs
By producing more products in shorter time
And reducing the energy required by using lower temperatures - change the properties of a product to make it more useful
Why are catalysts good for environmental sustainability
-Preserves energy
-Reduces waste
By producing fewer pollutants as higher at economy
Convert harmful pollutants into safer ones
What is Boltzmann distribution
The spread of molecular energies in gases
What does Boltzmann distribution curve show
Shows the different kinetic energies a number of molecules have in a substance
How does increasing temperature affect a Boltzmann distribution curve
Temperature increases the average energy of the molecules - molecules have higher energy
The graph will stretch
- the peak will be lower
- and further along the x axis
- area is the same
How do catalysts affect the Boltzmann distribution curve
Activation energy is lower on graph
More particles in effective collisions area
Dynamic equilibrium definition
The equilibrium that exists in a closed system when the rate of the froward reaction is equal to the rate of the reverse reaction and concentration do not change
Reverse reaction definition
A reaction that takes place in both the forward and reverse direction
Homogenous equilibrium definition
Equilibrium in which all of the reactants and products are present in a single solution (in the same phase)
What 3 things can change the position of equilibrium
Concentration
Pressure
Temperature
Le chapeliers principle
When a system in dynamic equilibrium is subjected to a external change, the system readjusts itself to…
minimise the effect of the change and restore equilibrium
Concentration rules
Le chateliers principle
When concentration of reactants increases
Shift to the side to get rid of that reactant
Minimise the extra reactant
When pressure increases
Chateliers principle
Shifts to the side with the fewest molecules
To minimise the increase in pressure
When temperature increases
Le chateliers principle
Shifts to endothermic direction
That absorbs this heat
To minimise the increases in temp
Catalyst effect on position of equilibrium
Has no effect
Just speeds up the rate of forwards and reverse reactions equally
Equilibrium reached faster
Why compromise temp in industries
Although low temp produces higher yield
The rate of reaction is too slow
So compromise between yield and faster reaction
Why compromise pressure
High pressure produces higher yield and rate of reaction
But is expensive and unsafe
Compromise between yield and expense
Equilibrium constant
Gives you an idea of how far to the left or right the equilibrium is
Kc = 1
Equilibrium =
Halfway between reactants and products
Kc > 1
Equilibrium =
Towards the products
Further to the right
Kc < 1
Towards the reactants
Further to the left
