Download 10th Class Chemistry Notes (Unit # 09) for Federal Board (FBISE) Islamabad

Download 10th Class Chemistry Notes (Unit # 09) for Federal Board (FBISE) Islamabad.

Very Easy, Updated & Comprehensive Notes for all types of students i.e. Average / Extra Ordinary

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Download 10th Class Chemistry Notes (Unit # 09) for Federal Board (FBISE) Islamabad

[Very Important] >> Question: Differentiate between forward and reverse reactions OR Describe the macroscopic characteristics of an equilibrium reaction.
Forward Reaction
Reverse Reaction
·         It is written from left to right.
·         Reactant produce products
·         Initially rate is fastest and gradually slows down.
·         It is written from right to left.
·         Products produce reactants.
·         Initially rate is zero and gradually speeds up.

[Important] >> Question: What is chemical equilibrium?
It is a state of a chemical reaction in which forward and reverse reactions take place at the same rate.

[Very Important] >> Question: State the law of Mass Action.
Two chemists C.M Guldberg and P. Waage in 1864 proposed this law. This law states that the rate at which:
  • A substance reacts is directly proportional to its active mass; and
  • The reaction proceed is directly proportional to the product of the active masses of the reactants.

[Very Important] >> Question: State the conditions for equilibrium.
i)             Concentration of none of the reactants or products is changed.
ii)           Temperature of the system is kept constant
iii)          Pressure or volume of the system is kept constant.

>> Question: What is the importance of equilibrium constant for a chemical reaction?
i)             It is used to determine the equilibrium concentration of equilibrium mixture.
ii)           It is used to predict the direction of a chemical reaction.
iii)          It is used to predict the extent of a chemical reaction.
iv)         It is used to predict the effect of change in conditions of the chemical reaction on equilibrium state.

[Important] >> Question: State the ways that equilibrium can be recognized?
  • It can be determined by determining concentration of reactants and products at regular intervals.
  • When constant concentration of products and reactants are observed, the reaction is at equilibrium.
  • This can be done by both physical methods as well as chemical methods such as titration, spectroscopy etc.

>> Following reaction can occur during lightening storms.
3O2 <----------------> 2O3
For this reaction write
a)      Equilibrium Constant Expression.
Kc     =      ------
b)      Determine the units of equilibrium constant
                [O3]2              []2
Kc     =      ------    =   ---------------       =      []-1         =      mole-1 dm3
                [O2]3              []3

c)      Forward and reverse reactions.
Forward Reaction        =      3O2 ----------------> 2O3
Reverse Reaction        =      2O3 ----------------> 3O2

Coal reacts with hot steam to form CO and H2. These substances react further in the presence of a catalyst to give methane and water vapour.
CO + 3H2 <---------------> CH4 + H2O
a)     Write forward and reverse reactions for it.
Forward Reaction        =      CO + 3H2 ---------------> CH4 + H2O
Reverse Reaction        =      CH4 + H2O ---------------> CO + 3H2
b)      Derive Kc expression for the reaction.
                [CH4] [H2O]
Kc     =      --------------
                [CO] [H2]3
c)      Determine units for Kc.
                [CH4] [H2O] [] []
Kc     =      -------------    =   ----------------------------               =      No Unit
                [CO] [H2]3                [] []
It has no unit because total number of moles of reactants is equal to the total number of moles of products.

>> Question: Write equilibrium constant expression for each of the following reactions.

H2O   <----------------------> H2 + ½O2
Kc     =      --------------
CO + 2H2 <----------------------> CH3OH
Kc     =      --------------

COCl2 <----------------------> CO + Cl2
Kc     =      --------------
4HCl + O2 <----------------------> 2Cl2 + 2H2O
Kc     =      ----------------

[Very Important] >> Question: Determine the units of equilibrium constants for the following reactions.

COCl2 <----------------------> CO + Cl2
                [CO][Cl2]            [][]
Kc     =      ------------  =      ------------------------------     = []
                [COCl2]                     []

H2 + I2 <----------------------> 2HI
                [HI]2                  []2
Kc     =      ------------  =      ------------------------------     = no unit
                [H2] [I2]                    [] []

2H2 + O2    <----------------------> 2H2O
                [H2O]2                        []2
Kc     =      ------------  =      ------------------------------     = []-1
                [H2]2 [O2]                 []2 []

        =      [mole-1.dm3]

N2 + 2O2   <----------------------> 2NO2
                [NO2]2                        []2
Kc     =      ------------  =      ------------------------------     = []-1
                [N2] [O2]2                 [] []2

        =      [mole-1.dm3]

[Very Important] >> Question: Bromine chloride (BrCl) decomposes to form chlorine and broine. For this reaction write i) chemical equation ii) Kc expression iii) Units of Kc.
Chemical Equation:
2BrCl <--------------------> Br2 + Cl2
Kc Expression:
Kc     =      ----------------------

Units of Kc:
                [Br2][Cl2]                    [][]
Kc     =      -------------------  =      -----------------------------      = no unit
                [BrCl]2                                   []2

[Very Important] >> Question: Kc expression for a reaction is given below. Write chemical equation for this reaction and derive the units of Kc.
Kc      =       ----------------------
Chemical Equation:
N2O4 <--------------------> 2NO2
Unit of Kc:
                [NO2]2                        []2
Kc     =      -------------------  =      -----------------------------      = []
                [N2O4]                                   []

[Important] >> Question: Cobalt chloride forms pink crystals (CoCl3.6H2O). When they are heated water is evolved and they turn blue (CoCl3). Explain how you could use Cobalt chloride as a test for water.
CoCl3.6H2O <-----------------------> CoCl3 + 6H2O
·         Anhydrous cobalt chloride paper is blue. But in water or any sort of moisture it starts to turn pink.
·         So if we are using it keep out of air. And don’t touch it with your hands because the moisture on your fingers would change the outcome of your cobalt chloride paper.

[Important] >> Question: Define complete reaction
A complete reaction is one in which all reactants have been converted to products.

[Very Important] >> Question: An understanding of equilibrium is important in the chemical industry why?
Equilibrium reactions are involved in some of the stages in the commercial production of many important chemicals such as ammonia, sulphuric acid etc.

[Very Important] >> Question: What happens when some liquid is placed in a closed container?
>> What is Reversible Reactions and Dynamic Equilibrium?
Some of the liquid undergoes a physical change by evaporating. As more liquid evaporates, some of the vapours condense due to collision with the surface of the liquid. Eventually the rate of evaporation equals the rate of condensation. At this stage equilibrium is established between forward and reverse changes.

[Very Important] >> Question: Define reversible reaction with examples.
A reaction in which the products can react together to reform the original reactants is called reversible reaction.
                                Fe / 450oC
N2 + 3H2            <--------------------------> 2NH3
                                200 atm

[Important] >> Question: Define equilibrium mixture
The concentrations of reactants and products are called equilibrium concentrations and the mixture is called equilibrium mixture.

[Important] >> Question: What do you know about formation of fizzy drinks? How this process interact with Equilibrium mixture.
When fizzy drinks are made, CO2 is dissolved in liquid drink under pressure and sealed. The forward reaction happens during manufacturing and reverse reaction happens on opening.

>> Question: What happens when SO2 and O2 gases are mixed in a sealed container?
Molecules of SO2 and O2 react to give SO3. Molecules of SO3 decomposes to give SO2 and O2.

[Important] >> Question: Define Active Mass.
The term active mass represents the concentration of reactants and products in moles dm-3 for a dilute solution, and is expressed in terms of square brackets [].

[Very Important] >> Question: Define Equilibrium Constant (Kc)
It is defined as the ratio of the product of concentration of products to the product of concentration of reactants each raised to the power equal to the coefficient in the balanced chemical equation.

>> What happens when we add water to concentrated sulphuric acid?
The addition of water to the concentrated sulphuric acid produces a vigorous reaction, which often causes acid droplets to spew in all directions. For this reaction this must be avoided. Always add the acid to water when diluting it.

[Very Important] >> Define Le Chatellier’s principle
If you impose a change in concentration, temperature or pressure on a chemical system at equilibrium, the system responds in a way that opposes the change.




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Download Class Notes: Download 10th Class Chemistry Notes (Unit # 09) for Federal Board (FBISE) Islamabad
Download 10th Class Chemistry Notes (Unit # 09) for Federal Board (FBISE) Islamabad
Download 10th Class Chemistry Notes (Unit # 09) for Federal Board (FBISE) Islamabad
Download Class Notes
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