equilibrium - unit 3 AOS 2 Flashcards
rate vs extent of a reaction
- rate is how much product id formed over a given period of time
- extent is the proportion of reactants that are converted into products
yield of a reaction
- yield is the amount of product that is obtained in a chemical reaction.
percentage yield = actual yield/theoretical yield x 100
dynamic equilibrium
- the rate of the forward reaction os equal to the rate of the reverse reaction
- there is not net change in reactants and products - they are produced at the same rate
- the concentrations of reactants and products remain constant but not necessarily equal
equilibrium constant K
- K is the value that gives an indication of the extent of a chemical reaction
- the larger the value of K, the more the reaction has proceeded.
- large K values indicate that the reaction proceeded significantly
- small K values indicate that the reaction only proceeded moderately.
- the only variable that will change the value of K is the temperature.
mixing reactants
- if reactants are mixed, the initial rate of the forward reaction will be greater than the reverse reaction
- at it decreases, the reverse reaction will increase until they are equal
homogenous reaction
the reaction occurs entirely within the same physical state
heterogenous reaction
a reaction that occurs between two physical states
equilibrium law
- the value of K is the ratio of the concentrations of the products to the concentrations of the reactions
calculating the K value
K= [products] / [reactants]
reverse reactions
- the value of K will be the reciprocal of the forward reaction
- In general, multiplying all reaction coefficients by 𝑥 causes K (and its unit) to be raised to the power of 𝑥.
coefficients changing
- In general, multiplying all reaction coefficients by 𝑥 causes K (and its unit) to be raised to the power of 𝑥.
using stoichiometry (nICE tables)
n= mole ratio
i = initial concentration
c= change in concentration
e= equalibrium concentration
steps
1. add mole ratios
2. add initial concentrations
3. use stoichiometry to calculate changes in concentration (products will be positive changes, reactants will be negative changes)
4. calculate equilibrium concentrations (initial - change)
reaction quotient
- a quantitative measure of how far towards completion a reaction has gone.
- if Q=K, the reaction is at equilibrium
- if Q is greater than K, the reverse reaction id favoured and more products will be converted into reactants
- if Q is less than K, the forward reaction is favoured and more reactants are converted into products.
- the higher the value of Q, the more products there are compare to reactants.
Le Chatliers Principle
- when a system at dynamic equilibrium is subject to change, the system will move to counteract this change and restore the system to equilibrium
adding reactants
- the forward reaction will be favoured and the reaction will shift to the right, creating more products to partially oppose the increase in reactants.
removing reactants
- the reverse reaction will be favoured and it will shift to the left, to partially oppose the decrease in reactants.
adding products
- the reverse reaction will be favoured, shifting to the left, to partially oppose the addition of products
removing products
- the forward reaction will be favoured, shifting to the right to partially oppose the decrease in products
changes to pressure/volume
- in increase in volume will decrease pressure
- a decrease in volume will increase pressure
- an increase in pressure causes the system to shift to the side will fewer particles, to oppose this increase in pressure
- a decrease in pressure will cause the system to shift to the side with more particles.
changes in temperature - exothermic reactions
- an increase in temperature causes the reverse reaction to be favoured, shifting to the left and the equilibrium constant will will decrease
- a decrease in temperature, causes the forward reaction to be favoured, shifting to the right and the equilibrium constant will increase
changes in temperature - endothermic
- an increase in temperature causes the forward reaction to be favoured, shifting to the right and the equilibrium constant will increase
- a decrease in temperature will cause the reverse reaction to be favoured, shifting to the left and the equilibrium constant will decrease.
the conflict between optimal rate and temperature
- increasing temperature increases the rate of reaction for most reactions
- however, for some reactions (exothermic reactions) the yield is higher when the temperature is lower
- therefore conditions need to be comprimised to ensure
- using high temperatures to produce a high rate and lower yield is more economically viable
using catalysts
- catalysts can be used to minimise the conflict between rate and temperature.
- catalysts only affect the rate and not the yield
- catalysts can be used to increase the rate of reaction for systems that require low energy for a higher yield to be produced.
how can an equilibrium system be made more efficient.
- The use of catalysts to increase the rate of reactions in industrial processes,
instead of high reaction temperatures. This dramatically reduces energy input, serving both an economic and environmental purpose; lower temperatures are less expensive and require less fuel to maintain - The use of heat exchangers to recover wasted heat from exothermic reactions
carried out on a large scale. This Transfers heat from one place to another, so heat energy given off by a reaction can be recovered and reused to continue powering the reaction, thereby reducing energy input requirements.
problems with high pressure
- expensive
- explosive
creating green hydrogen
the fuel and source of fuel needs to be green
- not of fossil fuel origin
