Lecture 5: Revison

Assertion (A): Liquids tend to have maximum number of molecules at their
surface.
Reason (R) : Small liquid drops have 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.

Assertion (A): At critical temperature liquid passes into gaseous state
imperceptibly and continuously.
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Exemplar Problems, Chemistry 62
Reason (R) : The density of 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.

Assertion (A): Gases do not liquefy above their critical temperature, even
on applying high pressure.
Reason (R) : Above 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.

Assertion (A): Gases do not liquefy above their critical temperature, even
on applying high pressure.
Reason (R) : Above critical temperature, the molecular speed is high and
intermolecular attractions cannot hold the molecules together
because they escape because of high speed.

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.

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.

In the following questions a statement of Assertion (A) followed by a statement
of Reason (R) is given. Choose the correct option out of the choices given
below each question.

Assertion (A): Three states of matter are the result of 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.

Match the graphs between the following variables with their names :
Graphs Names
(i) Pressure vs temperature                                                           (a) Isotherms
graph at constant molar volume.
(ii) Pressure vs volume graph                                     (b) Constant temperature curve
at constant temperature.
(iii) Volume vs temperature graph                                      (c) Isochores
at constant pressure.
                                                                                     (d) Isobars

Explain the effect of increasing the temperature of a liquid, on intermolecular
forces operating between its particles, what will happen to the viscosity of a
liquid if its temperature is increased?

Name two phenomena that can be explained on the basis of surface tension.

One of the assumptions of kinetic theory of gases is that there is no force of
attraction between the molecules of a gas.
State and explain the evidence that shows that the assumption is not applicable
for real gases.

Name two intermolecular forces that exist between HF molecules in liquid
state.

Name the energy which arises due to motion of atoms or molecules in a body.
How is this energy affected when the temperature is increased?

Pressure exerted by saturated water vapour is called aqueous tension. What
correction term will you apply to the total pressure to obtain pressure of
dry gas?

One of the assumptions of kinetic theory of gases states that “there is no force
of attraction between the molecules of a gas.” How far is this statement correct?
Is it possible to liquefy an ideal gas? Explain.

Value of universal gas constant (R) is same for all gases. What is its physical
significance?

Two different gases ‘A’ and ‘B’ are filled in separate containers of equal capacity
under the same conditions of temperature and pressure. On increasing the
pressure slightly the gas ‘A’ liquefies but gas B does not liquify even on applying
high pressure until it is cooled. Explain this phenomenon.

A gas that follows Boyle’s law, Charle’s law and Avogadro’s law is called an
ideal gas. Under what conditions a real gas would behave ideally?

What will be the molar volume of nitrogen and argon at 273.15K and 1 atm?

Use the information and data given below to answer the questions (a) to (c):
• Stronger intermolecular forces result in higher boiling point.
• Strength of London forces increases with the number of electrons in the
molecule.
• Boiling point of HF, HCl, HBr and HI are 293 K, 189 K, 206 K and
238 K respectively.
(a) Which type of intermolecular forces are present in the molecules
HF, HCl, HBr and HI?
(b) Looking at the trend of boiling points of HCl, HBr and HI, explain
out of dipole-dipole interaction and London interaction, which one
is predominant here.
(c) Why is boiling point of hydrogen fluoride highest while that of
hydrogen chloride lowest?

The behaviour of matter in different states is governed by various physical
laws. According to you what are the factors that determine the state of matter?

The boiling points of a liquid rises on increasing pressure. Give reason.

Some tiny light hollow spheres are placed in a flask. What would happen to
these spheres, if temperature is raised?

What is the effect of temperature on
(i) density
(ii) vapors pressure of a liquid?

Why is glycerol highly viscous?

Why are tyres of automobiles inflated to lesser pressure, in summer than in
winter?

Why does viscosity of liquids decrease as the temperature is raised?

How does surface tension change when temperature is raised?

What is surface tension? What is its S.I unit?

What is surface energy?

Define standard boiling point.

What is the value of compressibility factor Z, of a gas when
(i) pressure is low,
(ii) pressure is high,
(iii) at intermediate pressure.

Calculate the pressure exerted by one mole of CO₂ at 273 k if the Van der

waal’s constant a = 3.592 dm⁶ at m mol-1. Assume that the volume occupied by

CO₂ molecules is negligible.

Define Boyle point.

When does a gas show ideal behaivour in terms of volume?

Mention the two assumptions of kinetic theory of gases that do not hold good.

How are Van der waal’s constants ‘a’ and ‘b’ related to the tendency to liquefy?

Under what conditions do real gases tend to show ideal gas behaivour?

What property of molecules of real gases is indicated by van der waal’s
constant ‘a’?

Out of NH₃ and N₂, which will have (i) larger value of ‘a’ and (ii) larger value of

‘b’?

Write Van der waal’s equation for n moles of a gas.

Molecule A is twice as heavy as the molecule B. which of these has higher kinetic
energy at any temperature?

Explain how the function pv/RT can be used to show gases behave non-ideally
at high pressure.

What is the value of R at STP?

What is aqueous tension?

Calculate the volume occupied by 5.0 g of acetylene gas at 500C and 740mm
pressure.

At 250C and 760 mm of Hg pressure a gas occupies 600ml volume. What will be
its pressure at a height where temperature is 100C and volume of the gas is
640mL.

Deduce the relation pv = nRT where R is a constant called universal.

Define an ideal gas.

State Avogadro’s Law. Is the converse of Avogadro’s law true?

State the law depicting the volume-temperature relationship

50 cm³ of hydrogen gas enclosed in a vessel maintained under a pressure of

1400 Torr, is allowed to expand to 125 cm³ under constant temperature

conditions. What would be its pressure?

Define absolute zero temperature.

How is the pressure of a given sample of a gas related to temperature at
volume?

At what temperature will the volume of a gas at 00 c double itself, pressure
remaining constant?

Why helium and hydrogen gases not liquefied at room temperature by
applying very high pressure?

Define Boyle’s law.

What are the factors responsible for the strength of hydrogen bonds?

Define thermal energy.

Ice has lower density than water. Give reason.

What type of bond exists between H₂ O,HF, NH₃, C₂H₅ OH molecule.?

Give an example to show dipole-dipole forces.

Define Van der waal’s forces.

Explain the physical significance of Van der Waals parameters.

Critical temperature for carbon dioxide and methane are 31.1 °C and -81.9 °C respectively. Which of these has stronger intermolecular forces and why?

In terms of Charles' law explain why -273°C is the lowest possible temperature.

What would be the SI unit for the quantity pV²T ²/n?

A mixture of dihydrogen and dioxygen at one bar pressure contains 20% by weight of dihydrogen. Calculate the partial pressure of dihydrogen.

2.9 g of a gas at 95 °C occupied the same volume as 0.184 g of dihydrogen at 17 °C, at the same pressure. What is the molar mass of the gas?

Calculate the volume occupied by 8.8 g of CO₂ at 31.1°C and 1 bar pressure.

R = 0.083 bar L K^-1 mol^-1.

Pay load is defined as the difference between the mass of displaced air and the mass of the balloon. Calculate the pay load when a balloon of radius 10 m, mass 100 kg is filled with helium at 1.66 bar at 27°C. (Density of air = 1.2 kg m^-3 and R = 0.083 bar dm³ K^-1 mol^-1).

Calculate the total pressure in a mixture of 8 g of dioxygen and 4 g of dihydrogen confined in a vessel of 1 dm3 at 27°C. R = 0.083 bar dm3 K-1 mol-1.

How much time would it take to distribute one Avogadro number of wheat grains, if 10¹⁰ grains are distributed each second?

Calculate the total number of electrons present in 1.4 g of dinitrogen gas.

Calculate the temperature of 4.0 mol of a gas occupying 5 dm³ at 3.32 bar.

(R = 0.083 bar dm³ K^-1 mol^-1).

A student forgot to add the reaction mixture to the round bottomed flask at 27 °C but instead he/she placed the flask on the flame. After a lapse of time, he realized his mistake, and using a pyrometer he found the temperature of the flask was 477 °C. What fraction of air would have been expelled out?

34.05 mL of phosphorus vapour weighs 0.0625 g at 546 °C and 0.1 bar pressure. What is the molar mass of phosphorus?

Density of a gas is found to be 5.46 g/dm³ at 27 °C at 2 bar pressure. What will be its density at STP?

What will be the pressure of the gaseous mixture when 0.5 L of H₂ at 0.8 bar and 2.0 L of dioxygen at 0.7 bar are introduced in a 1L vessel at 27°C?

What will be the pressure exerted by a mixture of 3.2 g of methane and 4.4 g of carbon dioxide contained in a 9 dm³ flask at 27 °C ?

The drain cleaner, Drainex contains small bits of aluminum which react with caustic soda to produce dihydrogen. What volume of dihydrogen at 20 °C and one bar will be released when 0.15g of aluminum reacts?

Pressure of 1 g of an ideal gas A at 27 °C is found to be 2 bar. When 2 g of another ideal gas B is introduced in the same flask at same temperature the pressure becomes 3 bar. Find a relationship between their molecular masses.

At 0°C, the density of a certain oxide of a gas at 2 bar is same as that of dinitrogen at 5 bar. What is the molecular mass of the oxide?

Using the equation of state pV = nRT; show that at a given temperature density of a gas is proportional to gas pressurep.