Chapter 5: States of Matter

Q44Written answer

Assertion (A): Three states of matter are the result of a balance between

intermolecular forces and thermal energy of the molecules.

Reason (R): Intermolecular forces tend to keep the molecules together but

thermal energy of molecules tends to keep them apart.

(i) Both A and R are true and R is the correct explanation of A.

(ii) Both A and R are true but R is not the correct explanation of A.

(iii) A is true but R is false.

(iv) A is false but R is true.

Show solutionHide solution

Worked solution

Option (i) is correct.

Q45Written answer

Assertion (A): At constant temperature, pV vs V plot for real gases is not a

straight line.

Reason (R): At high pressure, all gases have Z > 1 but at intermediate

pressure most gases have Z < 1.

(i) Both A and R are true and R is the correct explanation of A.

(ii) Both A and R are true but R is not the correct explanation of A.

(iii) A is true but R is false.

(iv) A is false but R is true.

Show solutionHide solution

Worked solution

Option (ii) is correct.

Q46Written answer

Assertion (A): The temperature at which vapour pressure of a liquid is equal

to the external pressure is called boiling temperature.

Reason (R): At high altitude atmospheric pressure is high.

(i) Both A and R are true and R is the correct explanation of A.

(ii) Both A and R are true but R is not the correct explanation of A.

(iii) A is true but R is false.

(iv) A is false but R is true.

Show solutionHide solution

Worked solution

Option (iii) is correct.

Q47Written answer

Assertion (A): Gases do not liquefy above their critical temperature, even

on applying high pressure.

Reason (R): Above the critical temperature, the molecular speed is high and

intermolecular attractions cannot hold the molecules together

because they escape because of high speed.

(i) Both A and R are true and R is the correct explanation of A.

(ii) Both A and R are true but R is not the correct explanation of A.

(iii) A is true but R is false.

(iv) A is false but R is true.

Show solutionHide solution

Worked solution

Option (i) is correct

Q48Written answer

Assertion (A): At the critical temperature, the liquid passes into a gaseous state

imperceptibly and continuously.

Reason (R): The density of the liquid and gaseous phase is equal to critical

temperature.

(i) Both A and R are true and R is the correct explanation of A.

(ii) Both A and R are true but R is not the correct explanation of A.

(iii) A is true but R is false.

(iv) A is false but R is true.

Show solutionHide solution

Worked solution

Option (i) is correct.

Q49Written answer

Assertion (A): Liquids tend to have a maximum number of molecules at their

surface.

Reason (R): Small liquid drops have a spherical shape.

(i) Both A and R are true and R is the correct explanation of A.

(ii) Both A and R are true but R is not the correct explanation of A.

(iii) A is true but R is false.

(iv) A is false but R is true.

Show solutionHide solution

Worked solution

Option (iv) is correct.

VI. Long Answer Type

Q50Written answer

Isotherms of carbon dioxide at various temperatures are represented in Fig. 5.5. Answer the following questions based on this figure.

(i) In which state will CO2 exist between the points a and b at temperature T1?

(ii) At what point will CO2 start liquefying when temperature is T1?

(iii) At what point will CO2 be completely liquefied when the temperature is T2.

(iv) Will condensation take place when the temperature is T3.

(v) What portion of the isotherm at T1 represent liquid and gaseous CO2

at equilibrium?

Show solutionHide solution

Worked solution

(i) CO2 exists as in the gaseous state between the points ‘a’ and ‘b ’at temperature T1 because from point ‘a’ to ‘b’ volume starts decreasing and the pressure increases and the gaseous molecules start to come closer but exist in the gaseous state only.

(ii) At the temperature, T1 CO2 starts liquefying at the point ‘b’. Because at point ‘b’ the liquefication has just started or commences.

(iii) At the temperature T2, CO2 will be completely liquefied at the point ‘g’. Because in the curve at the temperature T2 point ‘f’ to ‘g’ represents the phase where the gas is being converted to liquid and at point ‘g’ all the gas has been converted to liquid.

(iv)As stated in the graph T3 > TC > T2 > T1. Temperature T3 > TC i.e. the critical temperature so condensation will not take place when the temperature is T3. Because critical temperature is the temperature of gas above which gas cannot be liquified howsoever high pressure is applied and T3 is greater than TC.

(v)At the temperature T1 curve the equilibrium of liquid and gaseous state of CO2 is represented between the point’s ‘b’ and ‘c’. Because between the points ‘b’ and ‘c’, the pressure being the constant volume of a gas decreases till point ‘c’ so between these points CO2 gas partially exists as in liquid and the gaseous state i.e. existing in equilibrium.

Q51Written answer

The variation of the vapour pressure of different liquids with temperature is shown in Fig. 5.6.

(i) Calculate graphically boiling points of liquids A and B.

(ii) If we take liquid C in a closed vessel and heat it continuously. At what temperature will it boil?

(iii) At high altitude, atmospheric pressure is low (say 60 mm Hg). At what temperature liquid D boils?

(iv) The pressure cooker is used for cooking food at the hill station. Explain in terms of vapour pressure why is it so?

Show solutionHide solution

Worked solution

(i) The boiling point of liquid A is: 315 K (approx.) and the boiling point of B is: 345 K (approx.)

(ii) In the closed vessel the liquid C will not boil because the pressure is kept on increasing in the vessel

(iii) According to the graph Temperature corresponding to 60mm of hg = 313 K. So liquid D will boil at 313 K.

(iv) Since the atmospheric pressure is low at high altitudes, water boils at low temperatures on hills. We already know that a liquid boils when its vapour pressure equals atmospheric pressure. Because a pressure cooker raises the boiling point of water and its heat content, food cooks faster.

Q52Written answer

Why does the boundary between the liquid phase and gaseous phase disappear on heating a liquid to critical temperature in a closed vessel? In this situation what will be the state of the substance?

Show solutionHide solution

Worked solution

The boundary between the liquid phase and gaseous phase disappear on heating a liquid up to critical temperature in a closed vessel because at the critical point the densities of liquid and the vapour become equal. The fluid at this stage is called ‘supercritical fluid’

Q53Written answer

Why does sharp glass edge become smooth on heating it to its melting point in a flame? Explain which property of liquids is responsible for this phenomenon.

Show solutionHide solution

Worked solution

Surface tension is the phenomenon responsible for this. The melted glass tends to take the minimum surface area that is sphere or spherical. On heating, the glass melts and it tends to take a round shape at the edge which has a minimum area.

My Cart

Your Cart 0

II. Multiple Choice Questions (Type-II)