The chemical reactions during which
material changes are accompanied with the change in heat energy are called thermo-chemical
reactions. The branch of chemistry which deals with the study of heat changes
in chemical reactions is Thermo chemistry and the reactions are called
thermochemcial reactions which are:
·Exothermic
reaction
·Endothermic
reaction
Q#
Questions
Year
Q#
01
What is thermochemcial reaction?
[2009] [2007]
Q#
02
Define Exothermic Reaction with example
[2017][2014][2011] [2010] [2007] [2006]
Q#
03
Define Endothermic Reaction with
example.
[2017][2016][2014] [2012][2010][2007]
[2006]
Q#
04
Define Enthalpy
[2016][2015][2013][2011] [2009][2007]
Q#
05
Define Thermo chemistry
[2013][2007]
Q. Define Thermochemistry and
thermochemical equation.
THERMO
CHEMISTRY
The branch of chemistry concerned with the
quantities of heat evolved or absorbed during chemical reactions is called
thermo chemistry.
THERMO
CHEMICAL EQUATION
Thermo chemical Equation is a balanced
stoichiometric chemical equation which includes the change in enthalpy, ΔH. In
variable form, a thermochemcial equation would look like this X + Y → Z
ΔH = (±) #
Where {X, Y, Z} are the standard agents of a chemical
equation with coefficients and “(±) #” is a positive or negative numerical
value, usually with units of KJ.
Q. What is heat of reaction?
HEAT OF
REACTION
Amount of heat evolved or absorbed during a chemical reaction is
called heat of reaction.
Q. Define exothermic reaction
and endothermic reaction. Give examples of each.
EXOTHERMIC
REACTION
Those reactions which accompanied with the emission of energy are
called exothermic reaction.
During exothermic reaction, heat energy is released because total
internal energy is greater than the total energy of the products. Change of
heat represents by ∆H with negative sign.
It usually forms the bond.
FOR
EXAMPLE
Reactant→Product + Heat
C + O2→CO2ΔH= -393.7 K.J/mol
H2 + ½ O2→H2OΔH= -286 K.J/mol
CH4 + 2O2→CO2 + 2H2O ΔH= -890 K.J/mol
ENTHALPY
FOR EXOTHERMIC REACTION
If enthalpy of product is smaller than enthalpy of reactants than
∆H will be negative and heat is evolved.
H2 + ½ O2→H2OΔH=
-286 K.J/mol
APPLICATIONS
OF EXOTHERMIC REACTION
To warm
the food contents
The armed forces don’t use fire to warm their foods. Their food
pouches contains flameless radiation heater. The heater contains chemicals (Mg,
Fe, NaCl) which reacts with water to produce heat in order to , warm the food,
pouch is kept in a bag and water is added, thus the temperature of food reached
up to 60o C within 15 minutes.
Mg +2H2O→Mg(OH)2
+ H2ΔH= -3.53
K.J/mol
Reaction of Magnesium with water is slow because of formation of
MgO film. Its reactivity can be increased by the presence of Fe and common
salt.
ENDOTHERMIC
REACTION
Those reactions in which heat energy is absorbed are called
endothermic reaction.
During endothermic reaction, heat energy is taken in from the
surrounding to the system because total internal energy of the reactant is less
than the total energy of the products.
It usually breaks the bond.
FOREXAMPLE
Reactant + Heat→Product
H2O+ ΔH→H2 + ½ O2ΔH= +286 K.J/mol
½ N2 + ½ O2 →NO
ΔH= +90 K.J/mol
ENTHALPY
FOR ENDOTHERMIC REACTION
If enthalpy of product is greater than enthalpy of reactants than
∆H will be positive and heat is absorbed.
H2O →H2 + ½ O2ΔH=
+286 K.J/mol
∆H = H2 – H1,
where ∆H= change of enthalpy,
H1= heat content of reactant,
H2= heat content of product
Q. Distinguish between
exothermic reaction and endothermic reaction.
Exothermic
reaction
Endothermic
reaction
Heat is released
Heat is absorbed or gained
Represent by negative sign
Represent by positive sign
Usually bond formation occurs
Usually bond dissociates
Total energy of the system decreases
Total energy of the system increases
Combustion, addition, neutralization, single displacement
reactions are the examples.
Decomposition reaction is the example.
Q. What is Enthalpy?
ENTHALPY
The energy possesses by the substance is called heat content of
substance or enthalpy.
It represents by ΔH.
ΔH= ( H2-H1)
Change of enthalpy = Enthalpy of Product – Enthalpy of reactant
MEASUREMENT
OF ENTHALPY
Exothermic and endothermic reaction can be detected by knowing the
temperature of vessel before and after the reaction:
·Rise
in temperature indicates the exothermic reaction
·Fall
in temperature indicates the endothermic reaction
·∆H
value can be determined by Calorimeter.
SIGN OF
ENTHALPY
1.If
enthalpy of product is greater than the enthalpy of the reactant then the sign
of ΔH will be positive.
2.If
enthalpy of product is smaller than the enthalpy of the reactant then the sign
of ΔH will be negative.
NEUTRALIZATION
When acids react with base then salt and water is formed, the
process is called Neutralization.
By the 15thcentury,
chemists recognized a group of substance which had sour taste so they named it
to ACIDS. They also recognized the other group of substance which lead bitter
taste and were used as good cleaning agent called BASES.
In the next century, scientists found
that whenever Acids react with the Bases, it neutralizes it and form an ionic
compound which is simply termed as SALT.
Q#
Questions
Year
Q#
01
Define pH.
[2018][2015][2012]
[2008]
Q#
02
Define acids, bases and salts. Write one property of each.
[2013]
Q#
03
Write properties of acids.
[2012][2006]
Q#
04
What is salt? Discuss its types.
[2017][2012][2010] [2008]
Q#
05
What are Double salts? Describe.
[2018][2014][2012][2011] [2008] [2007]
Q#
06
Write name of any three double salts with their chemical
formulae.
What is a base? Write two chemical and three chemical properties
of base.
[2005]
Q#
12
State Lewis concept of acids and bases.
[2017][2016][2011][2008] [2006] [2005]
Q#
13
State Arrhenius theory of acids and bases.
[2009]
Q#
14
State Bronsted Lowry theory of ionization.
[2015] [2010][2007]
Q#
15
Mention the uses of potash alum.
[2009][2007]
Q#
16
Mention the uses of Carnalite.
[2007]
Q#
17
Mention the uses of Mohr’s salt.
[2007]
Q#
18
Mention the uses of Epsom salt.
[2010]
Q#
19
Mention the uses of NaHCO3.
[2012]
Q#
20
Mention the uses of Chrome alum.
[2007]
Q. Give the Physical properties
of acids.
PHYSICAL
PROPERTIES OF ACIDS
1.Acids
have sour taste.
2.They
change the color of methyl orange and blue litmus paper to red
3.Aqueous
acids conduct electricity.
4.Concentrated
acids can destroy skin and tissues.
5.They
react with bases to forms salts and water.
Q. Give the Chemical properties
of acids.
CHEMICAL PROPERTIES OF ACIDS
NEUTRALIZATION
Acids react with base to form salt and water.
HCl + NaOH ⟶ NaCl + H2O
REACTION
WITH METALS
Whenever acid react with metals, H2 gas liberates.
Zn + 2HCl ⟶ ZnCl2 + H2
REACTION
WITH CARBONATE AND BICARBONATES
Acids produce CO2 gas, when react with carbonates and
bicarbonates
Na2CO3 + 2HCl ⟶ 2NaCl
+ H2O + CO2
NaHCO3 +HCl ⟶ NaCl + H2O +
CO2
Q. Give the Physical properties
of bases.
PROPERTIES
OF BASES
1.They
have bitter taste
2.They
have slippery touch.
3.Bases
are electrolytes
4.Concentrated
bases can damage tissues and skin.
5.They
covert red litmus paper to blue
6.Base
reacts with acids to produce salt and water.
Q. Describe Arhenius theory of
acids and bases.
ARHENIUS
THEORY OF ACIDS AND BASES
Swedish chemist Svante Arhenius in 1887,
describe the acids and bases.
ACID An acid can be defined as a substance that yields H+
ions when dissolved in water.
ARHENIUS ACID HCl → H+ + Cl-
BASE A base can be defined as a substance that yields OH-
ion when dissolved in water.
ARHENIUS BASE NaOH → Na+ + OH-
Q. Describe Bronsted Lowry
theory of acids and bases.
BRONSTED-LOWRY
THEORY OF ACIDS AND BASES
This theory was proposed by two
scientists’ English chemist Lowry and Danish Chemist Bronsted in 1923.
HCl and hydronium ion (H3O+)
are proton donors which act as Bronsted Lowry acids whereas H2O and
NH3 are proton acceptors which act as proton acceptors.
HCl + H2O H3O+ + Cl-
ACID: Acid is a substance which has tendency to donate one or more
protons.
BRONSTED-LOWRY
THEORY OF ACID: A substance that can donate H+
BASE: Base is a substance having a tendency to accept the protons.
BRONSTED-LOWRY
THEORY OF BASE A substance that can accept H+
Q. Describe Lewis theory of
acids and bases.
LEWIS
CONCEPT OF ACIDS AND BASES
In 1923, G. N Lewis proposed a more
general concept of acids and bases.
ACID An acid is any specie which can accept a pair of electrons
BASE A base is any specie which can donate a
pair of electrons
LEWIS ACIDS An electron pair acceptor
LEWIS BASE An electron pair donor
Q. Define Neutralization,
acidity of base and basicity of acids.
NEUTRALIZATION
When acids react with base then salt and water is formed, the
process is called Neutralization.
Neutralization is example of both double displacement reaction and
exothermic reaction
The number of ionizable or replaceable (OH-) ions per
molecule is called acidity of the bases.
BASICITY
OF ACIDS
The number of ionizable or replaceable hydrogen atoms present in a
molecule of an acid is called Basicity of the acids.
Q. Define salts and its types.
SALT
Salt is a substance that forms by the neutralization of acid and
base.
OR
Ionic compound which is produced by the neutralization between acid
and base is called Salt.
REACTION
NaOH + HCl → NaCl + H2O
KOH + HNO3 → KNO3 + H2O
CLASSIFICATION
OF SALTS
Salts have been classified into following three main categories
1.Acidic
salt
2.Basic
salt
3.Normal
salts
ACIDIC SALTS
Salts which are formed by the partial neutralization of an acid by
the base are called acidic salt.
FOR
EXMAPLE
NaHSO4, KHCO3, NaHCO3 etc.
REACTION
NaOH + H2SO4 → NaHSO4 + H2O
BASIC
SALTS
Salts which are formed by the partial neutralization of base with
the acid are called Basic Salt.
FOR
EXMAPLE
Mg(OH)Cl, Zn(OH)Cl
REACTION
Mg(OH)2 +
HCl → Mg(OH)Cl + H2O
NORMAL
SALT
Salts which are formed by the complete neutralization of acids and
base are called normal salts.
FOR
EXMAPLE
NaCl, NaNO3, K2SO4
REACTION
NaOH + HCl → NaCl + H2O
Q. What are double salts?
DOUBLE SALT
When two specific salts are crystallized
together they form a salt known as Double salt.
FOR EXAMPLE
Potash alum: K2SO4(Al2SO4)324H2O
Mohr’s salt: FeSO4
(NH4)2 SO4 6H2O
Chrome alum: K2SO4Cr2(SO4)324H2O
Carnalite: KCl.
MgCl2.6H2O
Q. Describe the construction and
working of Castner Kellner cell. Also write the production of NaOH.
CASTNER KELLNER CELL [Production of NaOH]
PRINCIPLE
NaOH is prepared by the electrolysis of Brine
(aqueous solution of NaCl) in Castner Kellner Cell.
CONCENTRATION OF BRINE
25% mass/ mass
CONSTRUCTION OF CASTNER
KELLNER CELL
It is a rectangular tank of steel
Inside of tank is lined with ‘ebonite’
Anode is made of titanium
Flowing layer of mercury (Hg) at the
bottom of tank serves as cathode
PROCEDURE
IONIZATION OF NaCl
2NaCl ⟶ 2Na+ + 2Cl-
When electric current is passed through
brine, +ve and –ve ions migrate towards their respective electrodes. Na+
ions are discharged at mercury cathode. The sodium deposited at mercury form
Sodium Amalgam. The produced Chlorine at the anode is removed from the top of
the cell.
REACTION AT CATHODE
2Na+ + 2e-⟶ 2Na
Na forms amalgam
Na + Hg ⟶ Na/Hg
Na+ ions are discharged in
preference to H+ ions due to high over voltage.
Na+ / Na EP= -2.71 V
H+/ H EP= 0.00 V
REACTION AT ANODE
2Cl-⟶ Cl2 + 2e-
FORMATION OF NaOH
Amalgam shifts to another chamber called
‘denuder’, where it is treated with water to produce NaOH.
2Na/Hg + 2H2O 2NaOH + H2+ 2Hg
ADVANTAGES OF CASNTER KELLNER
CELL
·Obtained NaOH is highly pure
·Process is very efficient
·Possible reaction between NaOH and Cl2 is
avoided because NaOH is obtained in separated chamber
DISADVANTAGES
OF CASTNER KELLNER CELL
·High electricity consumption
·Environmental pollution due to escape of Hg vapors
Q. Write chemical properties of
sodium hydroxide.
CHEMICAL
PROPERTIES OF SODIUM HYDROXIDE
REACTION WITH ACIDS
For the
production of salts, sodium hydroxide can be treated with sulphuric acid,
hydrochloric acid, nitric acid.
2NaOH + H2SO4⟶ Na2SO4
+ H2O
NaOH + HCl ⟶ NaCl + H2O
NaOH + HNO3⟶ NaNO3
+ H2O
REACTION WITH METALS
Sodium
hydroxide reacts with certain metals like zinc, tin aluminium
2NaOH + Zn
⟶ Na2ZnO2
+ H2
2NaOH + Sn ⟶ Na2SnO2 + H2
2NaOH + Al
+ 2H2O ⟶ 2NaAlO2 + 3H2
REACTION WITH CARBON
DI OXIDE
It reacts
with carbon di oxide to produce sodium carbonate and water.
2NaOH + CO2⟶ Na2CO3
+ H2O
REACTION WITH
CHLORINE GAS
The
reaction of sodium hydroxide with chlorine gas results in the formation of
sodium salt of oxy acids.
2NaOH + Cl2⟶ NaOCl
+ NaCl + H2O
Q. Write physical properties of
sodium hydroxide.
PHYSICAL
PROPERTIES OF SODIUM HYDROXIDE
·It is highly insoluble in water
·It produces high amount of heat
·Its melting point is 3180 C
·Its density is 2.13 gm/ml
Q. Give the industrial
preparation of Sodium carbonate.
INDUSTRIAL
PREPARATION OF SODIUM CARBONATE
AMMONIA
SOLVAY PROCESS OR AMMONIUM SODA PROCESS
Industrially,
sodium carbonate is produced by Ammonia Solvay process
RAW
MATERIALS
The raw
materials which are needed for the production of Sodium carbonate are given
below:
·Sodium chloride (Brine)
·Lime stone (CaCO3)
·CO2
·Ammonium chloride (NH4Cl)
PROCEDURE
At first stage, a saturated solution of
sodium chloride is prepared which is also known as Brine.
Brine is
the 28% m/m solution of NaCl
Following
are the steps of the industry:
AMMONIATION
OF BRINE
In this
stage, saturated solution of NaCl i.e. brine is allowed to flow down from
ammoniating tower. The ammoniated tower is fitted with mushroom shaped baffles
which are designed to control the flow of brine and ensure the proper mixing
and saturation of ammonia.
CARBONATION
OF AMMINIATED TOWER
In this
step, ammoniated brine is allowed to trickle down a carbonating tower called ‘Solvay
tower’. Here, brine is fixed with carbon di oxide gas.
CaCO3⟶ CaO + CO2
CO2
reacts with ammonia to form ammonium carbonate
2NH3
+ CO2 + H2O ⟶ (NH4)2CO3
Ammonium
carbonate further reacts with CO2 to form ammonium bi carbonate
(NH4)2CO3
+ CO2 + H2O ⟶ 2NH4HCO3
Ammonium
bi carbonate then reacts with NaCl to form Sodium bi carbonate.
NH4HCO3
+ NaCl ⟶ NaHCO3 + NH4Cl
Due to the
exothermic nature of the above reactions, solubility of NaHCO3 increases. To
oppose this effect, lower part of Solvay tower is cooled first, precipitate of
NaHCO3 are separated by vacuum filtration and then washed to remove
ammonium salts.
CONVERSION
OF NaHCO3
TO Na2CO3
Sodium
bicarbonate is heated in rotary furnace called ‘Calciner’ to produce anhydrous
sodium carbonate or soda ash. Carbon di oxide is re-circulated to carbonation
tower.
2 NaHCO3⟶ Na2CO3
+ CO2 + H2O
RECOVERY
OF AMMONIA
The CaO
which obtained from the heating of CaCO3 is treated with water to
form Ca(OH)2
CaO + H2O ⟶ Ca(OH)2
Quick lime
is heated with NH4Cl to form NH3 and CaCl2 (by
product).
2 NH4Cl
+ Ca(OH)2⟶ CaCl2 + 2NH3
+ 2H2O
Ammonia is used again in this process.
Q. Give the physical properties of Sodium bi
carbonate.
PHYSICAL
PROPERTIES OF SODIUM BI CARBONATE
·It is bitter in taste
·Sparingly soluble in water
·It is white crystalline compound
·Its density is 2.11 gm/ ml
Q. Give the chemical properties of Sodium bi
carbonate.
CHEMICAL
PROPERTIES OF SODIUM BI CARBONATE
REACTION WITH ACIDS
Sodium bi
carbonate loses carbon di oxide and water to give sodium carbonate on heating.
NaHCO3
+ HCl ⟶ NaCl + H2O + CO2
ACTION OF HEAT
Sodium bicarbonate
loses carbon dioxide and water to give sodium carbonate on heating.
2NaHCO3⟶ Na2CO3
+ H2O + CO2
Q. Give the uses of Sodium bi carbonate.
USES OF
SODIUM BICARBONATE
·It is used in the preparation of effervescent
drinks.
·It is used in fire extinguishers.
·It is used in the textile, tanning, paper, ceramics
industries.
·It is used in medicine as antacid to neutralize the
acids.
Q. Give the physical properties of Sodium
carbonate.
PHYSICAL
PROPERTIES OF SODIUM CARBONATE
·It is highly soluble in water
·Sodium carbonate (Na2CO3) is an
odorless, grayish white hygroscopic powder.
·The melting point of Sodium carbonate is 1,564°F (851°C)
·Density of sodium carbonate 2.53 g/cm3
·It is soluble in water.
·The water solution of soda ash has a basic pH and a strong
alkaline taste. If it is placed in a slightly acidic solution, it decomposes
and forms bubbles. This effect, called effervescence
·It is used as cleaning agent in soap and detergents.
Q. Give the chemical properties of Sodium
carbonate.
CHEMICAL
PROPERTIES OF SODIUM CARBONATE
PRODUCTION OF SALTS
Sodium
carbonate can be decomposed to produce salts
Na2CO3
+ 2HCl ⟶ 2NaCl + H2O + CO2
Q. Write note on Copper Sulphate.
COPPER
SULPHATE [CuSO4.5H2O]
It is also known as cupric sulphate or blue vitriol or blue stone.
PREPARATION
By reacting copper with dilute sulphuric acid in presence of air
copper sulphate may produce.
2Cu + 2 H2SO4 + O2 →
2CuSO4 + 2 H2O
CuO and CuCO3 can also produce copper sulphate by
reacting with dilute H2SO4.
CuO + H2SO4 → CuSO4 + H2O
CuCO3 + H2SO4 →
CuSO4 + H2O + CO2
USES
1.It
acts as germicide and insecticide.
2.It
uses in paints and vaccines.
3.It
is use to kill fungus and molds.
4.It
is used in textiles, tanning, electric batteries, hair dyes and electroplating.
Q. Write note on Magnesium
Sulphate.
MAGNESIUM
SULPHATE [MgSO4.7H2O]
It is also known as Epsom salt.
PREPARATION
It can be prepared by the action of H2SO4
over magnesite [MgCO3], dolomite [MgCO3.CaCO3]
or heating kieserite [MgSO4] under pressure with water.
2.It
is used in manufacture of ceramics, glazed tiles and match boxes.
3.It
is used in dyes and tanning processes.
4.It
is used in fire proof fabrics
5.It
is used in filter paper industry
Q. Write note on Alum.
ALUM
If equi molar quantities of potassium sulphate and aluminium
sulphate are dissolved in water and the solution is allowed to evaporate.
Crystals of potash alum are produced.
K2SO2 + Al2(SO4)3
+ 24H2O → K2SO2 Al2(SO4)3
24H2O
USES OF
POTASH ALUM
1.It
is used in sizing of paper.
2.It
is used in medicines.
3.It
is used in purifying water
4.It
is used as mouth wash.
Q. Write chemical formula of
Carnalite. Also give its uses.
CARNALITE
KMgCl3·6(H2O)
USES OF
CARNALITE
·It is mostly used in fertilizers.
·It is an important source of potash
Q. Write chemical formula of
Chrome alum. Also give its uses.
