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Solutions for Chemistry, Class 7, ICSE
Define matter.
Matter is anything that has mass, occupies space and can be perceived by our senses.
What is the difference between mass and weight?
| Mass | Weight |
|---|---|
| The quantity of matter that a body contains is known as its mass. | Weight is the force with which the earth pulls a body towards itself. |
| Mass of a body does not change with place. It remains constant. | Weight changes from place to place. |
If an object weighs 6 N on earth what will be its weight on moon? What will be the change in its mass?
The weight of body on moon will be 1 N i.e. [6N x ] because the weight of body is times lighter on the moon than it is on earth.
There will be no change in its mass because mass of a body remains constant irrespective of its place.
Write your observation and conclusion for the following:
(a) When few marbles are put in a glass half filled with water.
(b) Ice is kept at room temperature.
(a) When few marbles are put in a glass half filled with water the water level rises up. This is because marble occupy space.
(b) When ice is kept at room temperature, it changes into water. The temperature of ice is lower than room temperature, so it absorbs heat from its surroundings and melts to form water.
State three main characteristics of the particles of matter.
The three main characteristics of the particles of matter are:
Differentiate between an atom and a molecule.
| Atom | Molecule |
|---|---|
| An atom is the smallest possible unit of matter that exhibits all the properties of that matter and may or may not have independent existence. | A molecule is the smallest unit of matter which exhibits all the properties of that kind of matter and also has an independent existence. |
| An atom of a matter is smaller than its molecule. | A molecule is bigger than atom as it is made up of two or more atoms. |
Define:
(a) Solid
(b) Liquid
(c) Gas
Give two examples of each type.
(a) Solid — A solid is that state of matter which has a definite shape and a definite volume. The two examples are gold, wood.
(b) Liquid — A liquid is that state of matter which has a definite volume but no definite shape. The two examples are water, alcohol.
(c) Gas — A gas is that state of matter which has neither a definite shape nor a definite volume. The two examples are hydrogen, oxygen.
Why are liquids and gases called as fluids?
The substances which can flow are known as fluids. Liquids flow from higher to lower level and gases flow in all directions, so they are called as fluids.
(a) Define interconversion of states of matter.
(b) Why do solids, liquids and gases differ in their physical state?
(c) Under what conditions do solids, liquids and gases change their state?
(a) The phenomenon of change of one state of matter into another and then back to the original state without any change in its chemical composition, is called interconversion of states of matter. It occurs due to change in temperature and pressure.
(b) Solids, liquids and gases differ in their physical state due to difference in their intermolecular space and intermolecular forces of attraction.
Solids have negligible intermolecular space as the molecules are closely packed and the force of attraction is maximum. In liquids the molecules are less tightly packed as compared to solids, so the intermolecular space is larger and force of attraction is weaker. In gases the molecules are far apart so the intermolecular space is very large and the force of attraction is the least.
(c) Solids, liquids and gases change their state by change in temperature and by applying pressure.
Give reasons:
When a stone is dipped in a glass containing some water, the level of water rises but when a spoon of sugar is added to it and stirred, the water level does not rise?
When a stone is dipped in a glass containing some water, the level of water rises because the stone is a bigger object and cannot be dissolved and adjusted between the intermolecular spaces of water. But when a spoon of sugar is added to it and stirred, the water level does not rise because the sugar particles are smaller and get adjusted between the intermolecular spaces present in water molecules.
Give reasons:
A drop of ink added to water in a glass turns the whole water blue.
A drop of ink added to water in a glass turns the whole water blue because the water and ink particles are always in continuous random motion and due to this motion the blue coloured particles of the ink spread all over and give blue colour to the water.
Fill in the blanks:
(a) Air is a matter because it has ............... and ............... and it can be ............... .
(b) The molecules are made up of ............... .
(c) The quantity of matter in an object is called its ............... .
(d) The state of matter with definite volume and definite shape is called ............... .
(e) The substances which can flow are called ............... .
(a) mass, volume, compressed
(b) atoms
(c) mass
(d) solid
(e) fluids
Name the terms for the following:
(a) The change of a solid into liquid.
(b) The force of attraction between the molecules of matter.
(c) The particles of matter which may or may not have independent existence.
(d) The process due to which a solid directly changes into its vapours.
(e) The change of vapour into a liquid.
(a) Melting
(b) Intermolecular force of attraction
(c) Atom
(d) Sublimation
(e) Condensation
Classify the following into solid, liquid and gas:
Coal, kerosene, wood, oxygen, sugar, blood, water vapour, milk, wax.
| Solid | Liquid | Gas |
|---|---|---|
| Coal | kerosene | oxygen |
| Wood | blood | water vapour |
| Sugar | milk | |
| Wax |