CHAPTER 2- CHEMICAL REACTION AND CHEMICAL EQUATION

CHAPTER 2- CHEMICAL REACTION AND CHEMICAL EQUATION

Q1: State law of conservation of mass (matter)? Give examples.

Ans.: During any process, mass is neither created nor destroyed this law was put forward by a French chemist, lavoiser in 1785.

This law states that:
Matter is neither created nor destroyed during a chemical reaction.
During a chemical reaction, the total mass of the product is equal to the total mass of the reactants.

Example no 1:
When a piece of iron is left in moist air its surface gradually turns brown, the object gets rusted and gains mass.
4Fe+3O22Fe2O3
The increase in mass is just the mass of oxygen.

Example no 2

When coal burns it leaves behind ash. The ash is lighter than coal. But the mass of coal will be equal to that of ash and the liberated carbon dioxide.
C+O2CO2

Q2: state exothermic and endothermic reaction with examples?

Ans: exothermic reaction:-Reaction in which heat energy is evolved is known as exothermic reaction in such reaction the system become warmer and neat potential energy of substances decreases. The enthalpy of product is less than the enthalpy of
reactants.
Examples:-
When unslaked calcium oxide is added to water. the water becomes warm with formation of
Slaked time . in this reaction heat energy is released.

Endothermic reaction:-Reaction in which heat energy is absorbed is known as endothermic reaction . in such reaction enthalpy of reactants is lower than those of product. Since energy
Is absorbed during reaction the temperature of reaction decreases. (example are)
Heat is absorbed in the decomposition of calcium carbonate. In this reaction heating must be continuous to decompose calcium carbonate.

Q3: What are different types of reaction? Give chemical reaction of each type?

Ans: Chemical reaction are of following types:

1: Simple decomposition :-In this reaction a single compound is decomposed into two or more simple substance.
2: Synthesis:-In this reaction two or more substance combine to from a single compound it is also known as addition reaction.
3: Displacement:-In this reaction an atom or radical displaced by another in a compound. Such reaction depend upon the electropositive or electronegative nature of an atom or radical to displaced another.
4: Double decomposition / displacement :-In this reaction the two reactants decomposed to form two new substances by exchanging their radicals.
5: Neutralization:-In this reaction , the hydrogen ion of an acid neutralized by the hydroxide ion of a base to from salt and water.
6: Hydrolysis:-In this reaction the salt of either weak acid and base dissolve in water to from acid and base.

Q4:Explain Laws of Chemical Combinations with example.

Ans: Laws of Chemical Combinations

There are four laws of chemical combinations these laws explained the general feature of chemical change. These laws are:

1. Law of Conservation of Mass

2. Law of Definite Proportions

3. Law of Multiple Proportions

4. Law Reciprocal Proportions
Antoine Lavoiser has rejected the worn out ideas about the changes that take place during a chemical reaction. He made careful quantitative measurements in chemical reactions and established that mass is neither created nor nor destroyed in a chemical change.
Law of Conservation of Mass
Statement

It is presented by Lavoiser. It is defined as:

“Mass is neither created nor destroyed during a chemical reaction but it only changes from one form to another form.”

In a chemical reaction, reactants are converted to products. But the total mass of the reactants and products remains the same. The following experiment easily proves law of conservation of mass.
Practical Verification (Landolt Experiment)

German chemist H. Landolt, studied about fifteen different chemical reactions with a great skill, to test the validity of the law of conservation of mass.

For this, he took H.shaped tube and filled the two limbs A and B, with silver nitrate (AgNO3) in limb A and Hydrochloric Acid (HCl) in limb B. The tube was sealed so that material could not escape outside. The tube was weighed initially in a vertical position so that the solution should not intermix with each other. The reactant were mixed by inverting and shaking the tube. The tube was weighed after mixing (on the formation of white precipitate of AgCl). He observed that weight remains same.

HCl + AgNO3 ———-> AgCl + NaNO3
Law of Definite Proportions
Statement

It is presented by Proust. It is defined as:

“When different elements combine to give a pure compound, the ratio between the masses of these elements will always remain the same.”

Proust proved experimentally that compound obtained from difference source will always contain same elements combined together in fixed proportions.

Example

Water can be obtained from different sources such as river, ocean, well, canal, tube well, rain or by the chemical combination of hydrogen and oxygen. If different samples of water are analyzed, it will have two elements, hydrogen and oxygen and the ratio between their mass is 1:8.
Law of Multiple Proportions
Statement

This law is defined as:

“When two elements combine to give more than one compounds, the different masses of one element, which will combine with the fixed mass of other element, will be in simple whole number ratio.”

Two different elements can combine to form more than one compound. They can do so by combining in different ratios to give different compounds.
Example

Hydrogen and oxygen combine with one another to form water (H2O) and hydrogen peroxide (H2O2). In water and hydrogen oxide 2 g of hydrogen combine with 16g and 32g of oxygen respectively. According to law of multiple proportions, the different masses of oxygen (16g and 32g) which have reacted with fixed mass (2g) of hydrogen will have a simple ratio between each other i.e. 16:32 or 1:2. It means that hydrogen peroxide contains double the number of oxygen atoms than water. This law proves this point of Dalton’s Atomic Theory that atoms do not break in a chemical reaction.

Law of Reciprocal Proportions
Statement

This law is defined as:

“When two element A, B combine separately, with the mixed mass of the third element E, the ratio in which these elements combine with E is either the same or simple multiple of the ratio in which A and B combine with each other.”
Example

Hydrogen and Nitrogen separately combine to form ammonia (NH3) and dinitrogen oxide (N2O), in these compounds, fixed mass of nitrogen is 14g and combines with 8 g of oxygen and 3 g of hydrogen. The ratio between the mass of oxygen and hydrogen is 8:3. Hydrogen and oxygen also combine with one another to form water (H2O). The ratio between hydrogen and oxygen in water is 16:2. These ratios are not same. Let us observe whether these ratios are simple multiple to each other or not following mathematical operation is carried out.

8:3 ::16:2

8/3 : 16/2

8/3 x 2/16

1/3 => 1:3

9th Class Chemistry Important Solved Short Notes for Exam 2013

9th Class Chemistry Important Solved Short Notes For Exam 2013

CHAPTER 1- INTRODUCTION TO CHEMISTRY

Chemistry

The branch of science which deals with the composition and properties of matter, changes in matter and the laws or principles which govern these changes is called Chemistry.

Q1: Define Chemistry also define the branches of chemistry?

Ans: Chemistry:-The branch of science which deals with the composition and properties of matter, changes in matter and the laws or principles which govern these changes is called Chemistry.

The five branches of chemistry are as follows:
1: Organic chemistry:-Organic chemistry is the study of carbon containing substances and the synthesis of such material. many consumer products are organic in nature.
2: Inorganic chemistry: Inorganic chemistry is the chemistry of element and their compounds except those of carbon-hydrogen compounds and their derivatives.

3: Physical chemistry: Physical chemistry is the branch of chemistry which deals with the forces and principles involved in the combination of atoms and molecules.
4: Analytical chemistry: Analytical chemistry is the study of method and techniques used to determined the kind and quantity of various component in a given substance.
5: Biochemistry: Biochemistry is the chemistry of living organisms such as plants and animals.

Q2: Define mass?
Ans : Mass:-The quantity of matter contained in a body is called its mass.
its SI unit is “kilogram” and its symbol is “m”.

Q3: Define volume?
Ans : Volume:- Space occupied by a body is known as volume.
its SI unit is “m3″ and its symbol is “v”.

Q4: Define density?
Ans: Density:-It is define as ratio between mass and volume. mass per unit volume is known as density.
mathematically: d=m
v
Its SI unit is kg/m3. density of solid and liquid usually expressed in g/cm3 and that of gases as g/dm3.

Q5: Define temperature?
Ans: Temperature:- Temperature is a measure of the intensity of heat. it is thus a measure of the degree of hotness and coldness in a body.

Q6: Define specific gravity?
Ans: Specific gravity:- The specific gravity of a substance is the ratio of its mass to the mass of an equal volume of water at a specified temperature.
Specific gravity = mass of substance
mass of an equal volume of water
specific gravity of a substance ia a ratio between two same quantities and then fore has no unit.

Q7: Define element?
Ans: Element:- An element is defined as a substance in which all the atoms are chemically identical having same atomic number. for example: iron: silver: gold: copper: oxygen: hydrogen: etc.

Q8: Define compound?
Ans: Compound:- A compound is pure substances which consist of two or more element chemically combined in a fixed proportion by mass. compound can be broken down by chemical method.
for example: water(H2O); salt(NaCl).

Q9: Define mixture?
Ans: Mixture:-A mixture contains two or more element which can easily be separated by physical method. the component doesn’t lose its chemical properties.
for example: soil; rock; etc

Q10: Define valency?
Ans: Valency:-The chemical combining capacity of an atom or an element with another element is called valency.

Q11: Define atom?
Ans: Atom:-It is the smallest particle of an element. it does not exist freely into nature. it is the unit of an element involved in a chemical reaction.

Q12: Define molecule?
Ans: Molecule:- It is the combination of two or more atom. it can exist freely in the nature.

Q13: Define mole?
Ans: Mole:-The weight of an atom or a molecule expressed in grams is known as one mole.

Q14: Define atomic mass?
Ans: Atomic mass:-The atomic mass of an element is the average relative mass of the isotopes of that element referred to the atomic mass of carbon which is taken as 12.0000 amu.

Q15: Define molecular mass?
Ans: Molecular mass:- The molecular mass of an element when it exists in the form of molecular or of a compound is the average mass of the molecular as compound to one atom of 12C6.

Q16: Define gram atomic mass?
Ans: Gram atomic mass:- The weight of an atom expressed in gram is called gram atomic mass. it is also called gram atom.

Q17: Define gram molecular mass?
Ans: Gram molecular mass:- The weight of molecule expressed in gram is called gram molecular mass .it is also called gram molecule.

Q18: Define Avogadro’s number (n)?
Ans: Avogadro’s number:-The number of particles contained in a mole is equal to 6.023*10 power 23 is known as Avogadro number.

Q19: Define low of constant composition with examples?
Ans: Low of constant composition:-Proust formulate the low of constant composition in 1799 as that every pure sample of a particular chemical compound contain the same element combined in the same fixed proportion. it is also called the low of definite proportions.

examples:
1, He obtained several samples of copper carbonate from different sources and also prepared it through different methods in his laboratory. he found whatever source of method of preparation was used, it always had the same proportion of copper, carbon and oxygen by mass.
2, He also mixed ten grams of lead with different amount of sulphur to make the grey solid lead sulphide. he always found that the lead sulphide had the same fixed percentage of lead and sulphur.

Q20: Define heterogeneous mixture?
Ans: Heterogeneous mixture: the mixture which do not have uniform composition throughout their mass, are called heterogeneous mixture.

Q21: Define homogenous mixture?
Ans: Homogenous mixture: mixtures having uniform composition are called homogenous mixture.

Q22: Differentiate between compound and mixture?
Ans:

Compound Mixture1:it is a pure substance. 1:it is an impure substance.
2:it cannot be separated by physical methods. 2:it can be separated into its components by simple physical methods.
3:element forming compound lose their original properties-s. 3:substance making up the mixture do not lose their original properties.
4:its composition is fixed. 4:its composition is not fixed.
5:the melting point and boiling point of compound are sharp and characteristic of each compound. 5:the melting point and boiling point of a mixture are not sharp.