1
Q
reversible reactions
A
- some chemical reactions occur in both forward and reverse directions → reversible reactions
- many reactions don’t proceed to completion
- physical changes are also reversible
- changes in states
2
Q
equilibrium
A
- some reversible reactions reach a point where the concentrations of reactants and products remain constant
- occur when the rate of the forward and reverse reactions are equal
- both reactions are still occurring, but there is no observable net change
- a state of equilibrium has been used when the overall concentration of reactants and products don’t change over time
3
Q
open vs closed systems
A
- open systems
- matter and energy can be exchanged between systems and surroundings
- closed systems
- only energy can be exchanged between system and surroundings
- equilibrium can only be reached in CLOSED SYSTEMS
4
Q
dynamic equilbrium
A
- equilibrium is described as being in the dynamic state (constant activity)
- forward and reverse reactions haven’t stopped → are occuring simultaneously at the same rate
- reaction is ‘incomplete’ and reactants and products are present in the equilibrium mixture
- molecular level
- bonds are constantly being broken and new bonds are being formed
- reactants and products continue to be converted from one to another
5
Q
reversibility of the reaction
A
- once product forms, reverse process may occur
- if the product particles collide with enough energy at the correct orientation, bonds may break and the original reactions may reform
6
Q
2 graphs for equilibrium
A
- rate vs time
- concentration vs time
- remember to double check the axis to check which graph is being shown
7
Q
observing extent of reaction using colour
A
if one of the products of reaction is coloured, progress of reaction can be monitored by observing a colour change
8
Q
observing extent of reaction using conductivity
A
- can be used if the reaction involves the production of ions
- different reactions proceed to different extents
- ratios of reactants to products are different for different equilibrium systems
- HCl: strong acid - easily ionised in water - higher conductivity
- CH3COOH: weak acid - doesn’t ionise easily → low conductivity
- HCl reaction will proceed to a greater extent even if starting concentrations of both are the same
9
Q
extent vs rate of reaction
A
- extent of reaction
- describes how much product is formed when the system reaches equilibrium
- won’t give any info on how fast a reacion will happen
- rate of reaction
- a measure of change in concentration of reactants and products oVer time
- rate will determine how quickly an equilibrium is reached
- in reversible reaction, the rate changes as the reaction progresses
10
Q
reaction quotient (Q)
A
- concentration fraction of the mixture
- measures the relative amounts of products and reactants present during a reaction at a particular point in time
- concentration of products divided by the concentration of the reactants
- the coefficient of the reactants and products form indices
11
Q
reaction quotient (Q) vs equilibrium constant (K)
A
- the reaction quotient can be calculated for any micture of reactants and products at any time during a reaction
- value of Q changes as the reaction progresses
- at equilibrium the value will become constant as concentrations no longer change - known as K
- uses concentrations at equilibrium
12
Q
equilibrium constant K
A
- will give a consistent value when reactions are in equilibrium despite the different concentrations
- is different for different chemical reactions and at different temperatures
13
Q
what does Q tell us
A
if the reaction quotient (Q) is GREATER than K
- the system will shift to the left to reach equilibrium
- there will be a net reverse reaction with more reactants formed
if the reaction quotient (Q) is SMALLER than K
- the system will shift to the right to reach equilibrium
- there will be a net forward reaction with more products formed
if the reaction quotient Q is the same as K
- the system is at equilibrium
14
Q
how pressure affects volume
A
volume of gas is inversely proportionate to its pressure
15
Q
total pressure
A
- sum of partial pressure
16
Q
changes to equilibrium systems
A
- the extent of a reaction is affected by the reaction conditions
- relative amounts of reactants and products at equilibrium is referred to as position of equilbrium
- are often changed to maximise production of a desired product
- don’t confuse w equilibrium constant (K) - only changed by temp
17
Q
le chateliers principle
A
- if an equilibrium system is subject to change, the system will adjust itself to partially oppose the effect of change
- establishes new equilibrium
- LCP doesn’t provide explanation for these changes
- useful generalisation to help predict effect of changes to equilibrium systems
18
Q
reactant/product change for equilibrium
A
adding a reactant
- formation of more products
- net forward reaction
- equilibrium position shifts to the right
adding a product
- formation of more reactants
- net reverse reaction
- equilibrium position shifts to left
removing a product
- formation of more products
- net forward reaction
- equilibrium position shifts to the right
19
Q
effect of changing pressure/volume
ON EQUILIBRIUM SYSTEMS
A
only affects equilibrium positions of systems in the gas phase not solid or liquid
- particles are too tightly packed for an increase in pressure to have a noticeable effect on volume
when pressure is increased
- LCP states that the system will respond by reducing the pressure
- position of equilibrium will favour the side of the reaction with the least number of gas particles
- increased pressure → decreased volume of container → increase in partial pressures → increase in concentration
explaining using equilibrium law
- if volume is halved - partial pressures of all reactants and product gases double so concentration doubles
- when there are equal numbers of reactant and product particles, change in pressure won’t shift the position of equilibrium
20
Q
effect of adding inert gas
A
- overall pressure is increased
- partial pressures and concentrations of reactants and products is unchanged
- no effect on reaction quotient
21
Q
effect of dilution
A
- adding water decreased the concentration
- this shifts positon of equilibrium toward the side that produces the greatest number of dissolved particles
22
Q
effect of increasing temp
on equilibrium systems
A
increasing temp
- exothermic
- increases the energy of the substances in the micture
- applying LCP, the reaction opposes the increase in energy by absorbing the energy
- reaction will move to the left producing more reactants
- concentration of reactants increase and concentration of products decrease
- K decreases
- endothermic
- increases the energy of the substances in the mixture
- applying LCP, the reaction opposes the increase in energy by absorbing the energy
- reaction will move to the right producing more products
- K increases
23
Q
effect of decreasing temp on position of equilibrium
A
- Exothermic
- decreases the energy of the substances in the mixture
- applying LCP, the reaction opposes the increase in energy by releasing the energy
- reaction will move to the right producing more products
- K increases
- endothermic
- decreases the energy of the substances in the mixture
- applying LCP, the reaction opposes the increase in energy by releasing the energy
- reaction will move to the left producing more reactants
- K decreases
24
Q
effect of catalyst on equilibrium
A
lowers activation energy for both the forward and reverse reaction by the same amount
SAME AMOUNT SPECIFICALLY FOR THE ACTIVATION ENERGY NOT THE REACTION RATE
- lower activation energy increases the number of effective collisions for both forward and reverse reactions
- increases rate of both equally
- will not affect the position of equilibrium or equilibrium constant
- will increase rate that equilibrium is reached - allow system to reach equilibrium more quickly
25
what does value of K mean
- indicates the **extent of a reaction at equilibrium**
- **how far the forward reaction proceeds to reach equilibrium** and the equilibrium **yield (**amount of products present at equilibrium)
26
K and relative proportions of reactant and products
**very large greater than 10^4**
- almost complete reaction occurs
- concentration of products are much higher than the concentration of reactants at equilibrium
**very small, less than 10^4**
- negligible reaction occurs
- concentration of products are much lower than the concentration of reactants at equilibrium
**between 10^-4 and 10^4**
- extent of reaction is significant
- considerable concentrations of both reactants and products are present at equilibrium
27
structuring equilibrium responses
- decide what change is immediately occurring
- explain how the system will oppose the change
- explain what effect that will have on the position of equilibirum, yield of products, or K - depends on qs
28
reversible vs irreversible reactions
* in reversible reaction, there is **continuous interconversion** between the chemicals on either side of the reaction equation.
* In an irreversible reaction, the reactants are converted to products, but the **products cannot be converted back to reactants.**
