This state is not static, the reactions still proceed at the same rate i.e. the number of moles of product produced in the forward reaction is equal to the number of moles of substance disappearing per second in the backward reaction.
After attaining the state of equilibrium the reaction does not stop though it may appear as if it has stopped. In fact, both the forward and backward reactions continue even after attaining the equilibrium. But the rate the forward reaction becomes equal to the rate of backward reaction. This means that if some products are formed from the reactants than an equal amount of products are converted back into reactants. As a result of this, the concentration of both the reactants and products become constant. Hence it is known as dynamic equilibrium.
When a chemical reaction continues to proceed but the number of reactants and products remains constant, it is called as dynamic equilibrium.
Types of Chemical Equilibrium
Homogeneous equilibrium:
In an equilibrium reaction when both the product and the reactants are present in the same phase, it is called as homogeneous equilibrium. For example,
N2(g) + 3H2(g) ⇋ 2NH3 (g)
2SO2(g) + O2(g) ⇋ 2SO3 (g)
Heterogeneous equilibrium:
In an equilibrium reaction when both the product and the reactants are present in a different phase, it is called as homogeneous equilibrium. For example,H2O(l) ⇋ H20(g)
CaCO3(s) ⇋ CaO(s) + CO2(g)
Law of chemical equilibrium:
The Law of chemical equilibrium states that;
At constant temperature and pressure, the rate of a chemical reaction is directly proportional to the molar concentration of the reactants to the molar concentration of the products both raised to a power equal to the corresponding stoichiometric coefficients as represented by the balanced chemical equations.
Characteristics of Chemical Equilibrium:
- At a given temperature, the measurable properties like pressure, concentration, density or color remain constant in chemical equilibrium.
- Chemical equilibrium can be attained from either side (forward and backward reactions).
- It can be attained in less time in the presence of a catalyst; however, a catalyst cannot affect chemical equilibrium as it only affects the rate of both the reactions, forward and backward, to the same extent.
- It is dynamic in nature.
Factors affecting chemical equilibrium:
According to Le Chatelier’s principle if a chemical reaction in equilibrium is subjected to certain factors, the equilibrium shifts. The factors affecting equilibrium are mentioned below:
- Change in concentration
- Change in pressure
- Change in Temperature
- Effect of a Catalyst
- Effect of addition of an Inert Gas
To know more about chemical equilibrium and details about the factors affecting a chemical equilibrium stay tuned with BYJU’S.
If we have to define equilibrium the most simple definition would be it is a point where the net external force as well as torque acting on the body about COM or any other point is zero. But to be more specific for a rigid body equilibrium means both rotational as well as translational equilibrium. For example consider the following situation:
In this case the body is in translational equilibrium but the two forces form a couple hence it is not in rotational equilibrium. So suppose for a rod kept on a table minimum number coplanar forces (having different line of actions) that must act so that body remains in equilibrium? So if we analyze with one force it can’t be either translational or rotational equilibrium, with two force translational is possible but not rotational but with three we can achieve both.
Equilibrium is classified as Dynamic or Static equilibrium. The next question is what static equilibrium is and how it is different from dynamic? So if the body is in equilibrium but continues to move with uniform velocity it is known as dynamic equilibrium. For example, a ball moving with uniform velocity. On the other hand, if the body is in equilibrium while being at rest it is termed as static equilibrium.
Equilibrium is also classified as stable, unstable and neutral. Let’s see what these mean. Stable equilibrium is one in which if the body is displaced from its equilibrium position then it tends to move towards that equilibrium point. For example a ball kept at the bottom of a hemisphere.While in case of unstable equilibrium, if it is displaced from that point the body tends to move away from that point. Consider a ball kept at the top of a sphere. If we slide it, the ball tends to roll away from the topmost point. Similarly in neutral equilibrium the body neither moves towards nor away from the equilibrium point. For example displace a ball kept on horizontal surface slightly.
If you still have any doubt on equilibrium get connected to Byjus.com and get answers to all your questions from our mentors 24 x 7.
STUDENT MIND TEST QUESTIONS
TOPIC : CHEMICAL EQUILIBRIUM
chemical equilibrium is the state in which both reactants and products are present in concentrations which have no further tendency to change with time. The chemical equilibrium is achieved when the rate of forward reaction is same as the reverse reaction.
1. Identify the most correct answer at each item from the alternatives provided.
i) Describes rate and factors that cause chemical reaction and affect rate of chemical reaction.
A: equilibrium reaction
B: reversible reaction.
C: chemical kinetics
D: equilibrium position
ii) Lowering of activation energy.
A: decrease rate of chemical reaction
B: make reacting particles to start reaction easily.
C: favours backward reaction
D: stops the chemical reactions.
iii) According to the Collision theory, chemical reaction only takes place when particles
A: collide B: break up C: bond. Warmed
iv) Even if reacting particles contact, they will not react if
A: they do not posses activation energy
B: they are cold
C: they are few in number
D: temperature increases
v) It favours forward reaction when temperature lowered
A: reaction of hot chemicals
B: acid base reaction
C: endothermic reaction
D: exothermic reaction
vi) It proceed in both forward and back ward directions.
A: chemical reactions B: chemical equilibrium
C: irreversible reaction D: reversible reaction
vii) Change of either temperature, pressure or concentration to the chemical reaction that is at equilibrium may cause
A: shift of equilibrium position
B: increase of time for completing the reaction
C: increase of rate of reaction
D: high consumption of reactants
viii) A simple reversible reaction
A: forward reaction is fast than backward direction
B: both forward and backward directions proceed at the
Same rate
C: change direction with change of conditions
D: its backward direction is fast than forward direction
ix) Increase of temperature to the chemical reaction
A: makes reacting particles closer
B: makes reacting particles disorganised
C: increase kinetic energy to the reacting particles
D: increase potential energy to the reacting particles
x) At a very law temperature the reaction rate slows down even if the reaction is
A: exothermic B: endothermic C: at high temperature D: reversible
2. Match list A and list B
List A
i) The contact process
ii) The Haber process
iii) Dissolving concentrated sulphuric acid in water
iv) Has effect to equilibrium reactions that involves gases
v) Speed up rate of chemical reaction
vi) Irreversible reaction
vii) Equilibrium point
viii) increases of temperature
ix) Rate of chemical reaction
x) Reversible reaction and equilibrium reaction
List B
A: proceed in only one direction
B: proceed in either direction
C: take place in the closed systems
D: water formation
E: obtained when the rate of forward dire
ction is equal to that of backward dire
ction
F: favours forward direction in endothermic reaction.
G: increase production of ammonia gas.
H: 1/time
I: sulphur trioxide production
J: a catalyst
K: exothermic reaction
L: pressure.
M: ammonia gas production
3. Explain the meaning of the following words:-
a) Chemical catalyst
b) Reversible reaction
c) Rate of chemical reaction
d) Irreversible reaction
e) Endothermic reaction
f) Exothermic reaction
4. State Le Chatelier's principle.
5. a) Mention factors that affect rate of chemical reaction.
b) Explain how factors mentioned in(5 a) above affect rate of chemical reaction.
6. Distinguish endothermic reaction from exothermic reaction.
7. List down the factors that affect equilibrium position.
8. What will happen to the equilibrium position?
Change of energy=-Ve.
(a) if temperature is lowered to the system
(b) if some ammonia gas removed from the system
(c) if pressure increased
9. Draw energy level profiles for endothermic reaction and exothermic reactions.
10. Form III students performed an experiment to determine rate of reaction from volume of hydrogen gas produced against time when zinc granules reacted with dilute hydrochloric acid and the following results were obtained.
(a) Draw graph of volume against rate (b) Calculate the rate of the chemical reaction.
(c) At what time high volume of hydrogen gas collected?
d) At what time did the experiment produced the largest volume of oxygen?
11. State one example for endothermic reaction and one for exothermic reaction.
12. Observe the chemical equation the state the effect of increase of pressure to the equilibrium position since the system is at equilibrium.
13.
Explain the effects of the conditions to the production of sulphur trioxide gas from reaction of sulphur dioxide and oxygen if the system is at equilibrium.
(a) increase of temperature
(b) increase of pressure
(c) removing some sulphur dioxide.
(d) adding a catalyst to the system.
14. State conditions that enable us to know if the chemical reaction is taking place.
ANSWERS:
1.
i) C vi) D
ii) B. vii) A
iii) A viii) B
iv) A ix) C
v) D x) A
2. i) I vi)A
ii) M vii) E
iii) K viii) F
iv) L ix) H
v) J x) C
3. a) is a substance which alters the rate of the chemical reaction and remain unchanged at the end of the reaction.
b) is a chemical reaction that proceed both forward and backward direction depending varying conditions such as temperature,pressure and concentration.
c) refers to ratio of the amount of substance used or produced to the time taken.
d) is a reaction that proceed in one direction.
e) is a reaction that absorbs energy from the surrounding in form of heat.
f) is reaction which releases energy to the surrounding in form of heat.
4. It states that "if the system is at equilibrium and one of the factors is changed, the equilibrium position shifts to minimise the effect of change and new equilibrium is established".
5. (a) factors which affect rate of chemical reaction are:-
-temperature
-concentration
-surface area
-catalyst
(b) Temperature
It affects rate of chemical reaction by increasing kinetic enerqy to reacting particles when it is increased to the system.
If the chemical reaction is endothermic, its rate increase with increase of temperature(vice versa is true)
If the chemical reaction is exothermic, its rate increase with decrease of temperature(vice versa is true)
Concentration.
It affects the rate of chemical reaction by increasing or lowering reacting particles.
The rate of the chemical reaction increase with increase of concentration( number of reacting particles). Vice versa is true.
Surface ares.
It affects rate of chemical reaction depending on the size of chemical substances.
Small size of chemical substance(powdered) makes higher surface area than the relative large size(granules)
The rate of chemical reaction increases with increase of surface area(vice versa is true)
Catalyst.
It affects the rate of chemical reaction by speeding up the reaction rate.
Presence of catalyst in the chemical reaction increase rate of chemical reaction.(vice versa is true)
6. -Endothermic reaction absorbs heat energy from the surrounding WHILE Exothermic reaction release heat energy to the surrounding.
-In an endothermic reaction, the products are formed at relative hing temperature WHILE in an exothermic reaction, the products are formed at relative low temperature.
-Endothermic reaction indicated by positive symbol of its energy change. (change of energy= +Ve) WHILE Exothermic reaction indicated by negative symbol of its energy change( change of energy= -Ve)
7. Factors that affect equilibrium position are:-
-Temperature
-Concentration
-pressure
TEMPERATURE
Effect of temperature if the reaction is endothermic.
When temperature increased to the system it favours forward reaction and if the Was at equilibrium, increase of temperature shifts equilibrium position to the right
In order to minimise the effect of change in the system.
Effect of temperature if the reaction is endothermic.
Lowering of temperature favours forward reaction hence equilibrium position shifts
or moves to right to minimise the effect of change in the system.
CONCENTRATION.
Concentration affects equilibrium position by favouring the side which have high concentration.
If there is high concentration to the reactant side forward reaction is favoured and equilibrium position shifts to the right. Vice versa is true.
PRESSURE.
Effects of pressure to the system depends on total volume or number of moles at each side of the reaction.
If at the product side(right) consists fewer number of moles , forward reaction is favoured and equilibrium position shifts to the right. Vice versa is true.
8. (a) lowering of temperature increase rate of forward reaction since the chemical reaction is exothermic.
Equilibrium position shifts forward.
(b) if some of ammonia gas removed from the system, the rate of backward reaction because at the left side concentration is lowered.
Equilibrium position shifts backward.
(c) increase of pressure speed up rate of forward reaction.
Equilibrium position shifts backward because it is a side that produce fewer molecules.
NB. Pressure has no effect if both sides of the equilibrium position have equal number of molecules.
9
 |
| Figure above show exothermic reaction |
10. (a)
(b) rate is calculated from the graph by obtaining the gradient as shown in 10 (a) above.
Gradient=rate
If the slope is steep it means the rate of reaction is high.
(c) at 180 second, high volume of the gas collected.
(d) in the first 20 seconds the largest volume of the gas produced because its slope is steep .
NB.
The scales of the graph are easily obtained by taking the highest value of the data dividing by the number of the lines that you prefer to use.
For example the highest value on vertical line is 66.
But i prefer to use 18 lines of the graph
To get scale interval.
66/18=4
4cm3 is the interval between two lines(one square)
11. - examples of endothermic Reactions are
*photosynthesis process
*water vapour formation process
- examples of exothermic reactions are
*explosion
* reaction of water an concentrated acid.
* combustion of fuel.
12. There is no effect to the equilibrium position because both sides of the equilibrium system have equal volume(number of moles).
13. (a) increase of temperature favours backward reaction since the reaction is exothermic. This makes low production of sulphur trioxide.
(b) increase of pressure favours forward reaction because to the product side there is fewer moles and low volume. This makes high production of sulphur trioxide gas.
(c) removal of some sulphur dioxide cause backward reaction due to decrease of concentration to the reactants side. This makes low production of sulphur trioxide gas.
(d) addition if a catalyst to the system does not affect the production of the sulphur trioxide gas because catalyst will speed up both forward reaction and backward reaction.
14. The conditions that enable us to know if the chemical reaction is taking place are.
-colour change of the mixture
-smell
-precipitation
-temperature change
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