A. Anything that has mass and occupies space is known as matter. All forms of matter are made up of molecules and molecules are made up of atoms.
State 3 properties of molecules of matter.
A. The three properties of molecules of matter are-
(i)They are very small in size.
(ii)They have spaces between them.
(iii)They are in constant motion as they posses kinetic energy.
What do you mean by inter molecular spaces ? How do Inter molecular spaces vary in different states of matter ?
A. Generally the spaces between molecules of matter is called inter molecular space. It is negligible in solids , more in liquids and still more in gases.
What is meant by inter molecular force of attraction ? How do they vary in solids liquids and gases ?
A. The molecules excret a force of attraction known as inter molecular force of attraction. solids have very strong inter molecular force , liquids have less inter molecular force and gases have negligible inter molecular force.
Which of the following are correct ?
A. (i) Solids have a definite volume and a definite shape. = Correct
(ii) Liquids have a definite volume but no definite shape. = Correct
(iii) Gases have a definite volume but no definite shape. = Wrong
(iv) Liquids have a definite volume and a definite shape. = Wrong
Discuss the three states of matter on molecular model.
A. All states of matter are made of very tiny particles called molecules . These molecules are very small in size and molecules can be further divided into smaller particles known as atoms. The space between two molecules(inter molecular space) is almost not there or negligible in solids , in liquids , it is more than solids and in gases it is very high. the molecules in solid can only vibrate in their mean position but in liquids molecules can move freely within the boundary of the container but in gas the molecules are free to move in the space available to them.
What do you mean by the term ‘the change of state’ ? Make a flow chart showing the complete cycle of change of state.
A. The process of change from one slate to another state either by absorption or rejection of heat at a constant temperature is called change of state.
Differentiate between melting point and boiling point giving at least one example.
A. MELTING POINT :- A fixed temperature at which a solid changes into its liquid state with the absorption of heat is known as melting point. For example ; the ice (solid) at 0’C melts to form water (liquid) by the absorption of heat.
BOILING POINT :- A fixed temperature at which a liquid changes into its gaseous state with the absorption of heat is known as boiling point. For example ; water (liquid) at 100’C changes into steam (gas) by the absorption of heat.
Describe the process of condensation and sublimation with examples.
A. CONDENSATION :- The change from a gas to its liquid state at a fixed temperature by the rejection of heat is known as condensation. For example ; steam (gas) at 100’C changes into water (liquid) by the rejection of heat.
SUBLIMATION :- The change from a solid directly to its gaseous state at a fixed temperature by the absorption of heat is known as sublimation. For example ; when camphor is heated it directly changes into vapours without changing into its liquid state.
Explain the term melting and melting point.
A. MELTING :- The change from a solid into its liquid state at a fixed temperature by the absorption of heat is known as melting. For example ; when ice is kept at room temperature for a specific period of time it changes into water.
MELTING POINT :- A fixed temperature at which a solid changes into its liquid state with the absorption of heat is known as melting point. For example ; the ice (solid) at 0’C melts to form water (liquid) by the absorption of heat.
Describe that substances absorb heat without any change in temperature during melting.
A. Take a test tube with some wax in it. clamp it to a vertical iron stand and place it over a wire gauze. Clamp a thermometer in the same manner in such a way that its bulb is inside the wax. Heat the arrangement over a burner and record the temperature after every minute.
We can notice that the wax melts at 55 degree Celsius during which the heat is supplied but the temperature doesn’t rise. Thus, the melting point of wax is 55 degree Celsius. After the whole wax is melted the temperature starts to rise again.
Explain the term vapourisation and boiling point.
A. VAPOURISATION :-The change from a liquid into its gaseous state at a fixed temperature by the absorption of heat is known as vapourisation. For example ; when water is boiled for a specific period of time it changes into steam.
BOILING POINT :- A fixed temperature at which a liguid changes into its gaseous state with the absorption of heat is known as boiling point. For example ; water (liquid) at 100 degree Celsius changes into steam (gas) by the absorption of heat.
A liquid can change into vapour state
(a)at a fixed temperature
(b)at all temperatures
Name the processes involved in the two cases.
Demonstrate with an example that water absorbs heat during boiling at a constant temperature.
A. When we boil water and record its temperature after every minute. we will notice that on coming to the temperature of 100 degree Celsius, its temperature does not increase but instead it is still absorbing heat. When its changed into vapours its temperature starts to rise again.
Thus, we can conclude that water absorbs heat even during boiling at a constant temperature.
State (a) The melting point of ice (b)The boiling point of water.
A.The melting point of ice is 0 degree Celsius and the boiling point of water is 100 degree Celsius.
What is evaporation?
A. Evaporation is another process by which a liquid changes into its gaseous state.
State three factors that effect the rate of evaporation of a liquid.
A.(i)The temperature of liquid
(ii)The presence of moisture or humidity
(iii)The flow of air above the liquid
Wet clothes dry more quickly on a warm dry day than on a cold humid day. Explain.
A.A wet cloth dries up on a hot day much faster than on a cold day. The rate of evaporation is higher if the temperature of liquid is higher.
Water in a dish evaporates faster than in a bottle.Give reason.
A.Because in a dish the surface area of the water increases and the evaporation becomes faster.
Volatile liquids are stored in tightly closed bottles. Give reason.
A. Volatile liquids like alcohol and spirits have low boiling points thus they evaporate much faster than water. This is the reason why volatile liquids are stored in tightly closed containers.
Why is cooling produced on evaporation of a liquids?
A. The reason why evaporation produces cooling is that a body requires heat to evaporate. The heat is supplied by its surroundings. Thus, it results in cooling of surrounding.
Explain with an example that when a liquid evaporates , it takes heat from its surroundings.
A. When sweat evaporates from our body it takes heat to evaporate from our body. It helps in maintaining our body temperature.
Give two applications of evaporation.
A. We often pour tea into the saucer to cool faster. when the tea is poured into the saucer its surface are increases and this leads to faster evaporation.
Explain why in hot summer days water remains cool in earthen pots.
A. Because water seeps out of the pores in the pot . The heat required for the water outside to evaporate is taken from the water inside the pot which therefore gets cooled.
A patient suffering from high fever is advised to put wet cloth strips on his forehead. Why?
A. When the water from the strip evaporates it takes the heat from the patients body therefore the temperature of the body decreases.
What do you mean by sublimation ? Explain with an example.
A. The change from a solid directly to its gaseous state at a fixed temperature by the absorption of heat is known as sublimation. For example ; when camphor is heated it directly changes into vapours without changing into its liquid state.
Why does the size of naphthalene balls decrease when left open ?
A. When left open the naphthalene balls sublimate into their vapour state and therefore their size decreases.
Demonstrate the process of sublimation with an example.
A. Take some camphor powder in a dish with an inverted funnel over it. Seal the ends of the funnel with a cotton piece. Then place the arrangement on a wire gauge on a tripod stand and heat it over a Bunsen burner. After sometime you will notice vapours of camphor which on rising get cooled and stick to the inner walls of the funnel.
Thus, we can conclude that camphor on heating changes directly from solid to its gaseous state without undergoing the liquid state. And its vapours on cooling directly change into solid camphor.