Chapter 15, Problem 100E

Classify each of the following statements as true or false.

a) Intermolecular attractions are stronger in liquids than in gases.

b) Substances with weak intermolecular attractions generally have low vapor pressures.

c) Liquids with high molar heats of vaporization usually are more viscous than liquids with low molar heats of vaporization.

d) A substance with a relatively high surface tension usually has a very low boiling point.

e) All other things being equal, hydrogen bonds are weaker than induced dipole or dipole forces.

f) Induced dipole forces become very strong between large molecules.

g) Other things being equal, nonpolar molecules have stronger intermolecular attractions than polar molecules.

h) The essential feature of a dynamic equilibrium is that the rates of opposing changes are equal.

i) Equilibrium vapor pressure depends on the concentration of a vapor above its own liquid.

j) The heat of vaporization is equal to the heat of fusion, but with opposite sign.

k) The boiling point of a liquid is a fixed property of the liquid.

l) If you break (shatter) an amorphous solid, it will break in straight lines, but if you break a crystalline solid, it will break in curved lines.

m) Ionic crystals are seldom soluble in water.

n) Molecular crystals are nearly always soluble in water.

o) The numerical value of heat of vaporization is always larger than the numerical value of heat of condensation.

p) The units of heat of fusion are $\text{kJ}/\text{g}\cdot °\text{C}$.

q) The temperature of water drops while it is freezing.

r) Specific heat is conerned with a change in temperature.

Interpretation Introduction

(a)

Interpretation:

Whether the statement, “Intermolecular attractions are stronger in liquids than in gases” is true or false is to be identified.

Concept introduction:

The interaction that exists between the molecules is called as intermolecular forces. The nature of forces present depends on the type of functional group present in the molecule. Different types of interactions present in covalent compounds are Van der Waal forces, dipole-dipole interactions and hydrogen bonding.

Answer to Problem 100E

The statement, “Intermolecular attractions are stronger in liquids than in gases” is true.

Explanation of Solution

In gases, particles are present very far from each other whereas in liquid, particles are tightly packed as compared to gases. This shows that the intermolecular forces of attraction are stronger in liquids than in gases.

Conclusion

The statement, “Intermolecular attractions are stronger in liquids than in gases” is true.

Interpretation Introduction

(b)

Interpretation:

Whether the statement, “Substances with weak intermolecular attractions generally have low vapor pressures” is true or false is to be identified.

Concept introduction:

The interaction that exists between the molecules is called as intermolecular forces. The nature of forces present depends on the type of functional group present in the molecule. Different types of interactions present in covalent compounds are Van der Waal forces, dipole-dipole interactions and hydrogen bonding.

Answer to Problem 100E

The statement, “Substances with weak intermolecular attractions generally have low vapor pressures” is false.

Explanation of Solution

The pressure exerted by the vapors of the liquid is known as vapor pressure. Substances that have weak intermolecular attractions move from liquid state to gaseous state easily. Therefore, substances with weak intermolecular attractions generally have high vapor pressures.

Conclusion

The statement, “Substances with weak intermolecular attractions generally have low vapor pressures” is false.

Interpretation Introduction

(c)

Interpretation:

Whether the statement, “Liquids with high molar heats of vaporization usually are more viscous than liquids with low molar heats of vaporization” is true or false is to be identified.

Concept introduction:

The interaction that exists between the molecules is called as intermolecular forces. The nature of forces present depends on the type of functional group present in the molecule. Different types of interactions present in covalent compounds are Van der Waal forces, dipole-dipole interactions and hydrogen bonding.

Answer to Problem 100E

The statement, “Liquids with high molar heats of vaporization usually are more viscous than liquids with low molar heats of vaporization” is true.

Explanation of Solution

In high viscous liquid, particles are tightly packed and the intermolecular forces of attraction between them are strong. As a result large amount of heat is required for the vaporization of more viscous liquid than less viscous liquid.

Conclusion

The statement, “Liquids with high molar heats of vaporization usually are more viscous than liquids with low molar heats of vaporization” is true.

Interpretation Introduction

(d)

Interpretation:

Whether the statement, “A substance with a relatively high surface tension usually has a very low boiling point” is true or false is to be identified.

Concept introduction:

The interaction that exists between the molecules is called as intermolecular forces. The nature of forces present depends on the type of functional group present in the molecule. Different types of interactions present in covalent compounds are Van der Waal forces, dipole-dipole interactions and hydrogen bonding.

Answer to Problem 100E

The statement, “A substance with a relatively high surface tension usually has a very low boiling point” is false.

Explanation of Solution

The intermolecular forces of attraction between particles of liquid, which have high surface tension, are very strong. High temperature is required is break these intermolecular forces of attraction. Therefore, a substance with a relatively high surface tension usually has a high boiling point.

Conclusion

The statement, “A substance with a relatively high surface tension usually has a very low boiling point” is false.

Interpretation Introduction

(e)

Interpretation:

Whether the statement, “All other things being equal, hydrogen bonds are weaker than induced dipole or dipole forces” is true or false is to be identified.

Concept introduction:

The interaction that exists between the molecules is called as intermolecular forces. The nature of forces present depends on the type of functional group present in the molecule. Different types of interactions present in covalent compounds are Van der Waal forces, dipole-dipole interactions and hydrogen bonding.

Answer to Problem 100E

The statement, “All other things being equal, hydrogen bonds are weaker than induced dipole or dipole forces” is false.

Explanation of Solution

The order of strength of intermolecular forces of attraction is shown below.

$\text{Ion-dipole}>\text{hydrogen}\text{bond}>\text{dipole-dipole}>\text{dipole-induced}\text{dipole}$

Therefore, the hydrogen bonds are stronger than the induced dipole or dipole forces of attraction.

Conclusion

The statement, “All other things being equal, hydrogen bonds are weaker than induced dipole or dipole forces” is false.

Interpretation Introduction

(f)

Interpretation:

Whether the statement, “Induced dipole forces become very strong between large molecules” is true or false is to be identified.

Concept introduction:

The interaction that exists between the molecules is called as intermolecular forces. The nature of forces present depends on the type of functional group present in the molecule. Different types of interactions present in covalent compounds are Van der Waal forces, dipole-dipole interactions and hydrogen bonding.

Answer to Problem 100E

The statement, “Induced dipole forces become very strong between large molecules” is true.

Explanation of Solution

In large molecules, atoms are surrounded by same or different atoms. The probability of development of induced dipole is more in large molecules. Therefore, induced dipole forces become very strong between large molecules.

Conclusion

The statement, “Induced dipole forces become very strong between large molecules” is true.

Interpretation Introduction

(g)

Interpretation:

Whether the statement, “Other things being equal, nonpolar molecules have stronger intermolecular attractions than polar molecules” is true or false is to be identified.

Concept introduction:

The interaction that exists between the molecules is called as intermolecular forces. The nature of forces present depends on the type of functional group present in the molecule. Different types of interactions present in covalent compounds are Van der Waal forces, dipole-dipole interactions and hydrogen bonding.

Answer to Problem 100E

The statement, “Other things being equal, nonpolar molecules have stronger intermolecular attractions than polar molecules” is false.

Explanation of Solution

The net dipole moment of nonpolar and polar molecules is $0$ and $>0$, respectively. Therefore, intermolecular forces of attraction between them are more than the nonpolar molecules.

Conclusion

The statement, “Other things being equal, nonpolar molecules have stronger intermolecular attractions than polar molecules” is false.

Interpretation Introduction

(h)

Interpretation:

Whether the statement, “The essential feature of a dynamic equilibrium is that the rates of opposing changes are equal” is true or false is to be identified.

Concept introduction:

At the dynamic equilibrium, the rate of conversion of reactant to product and rate of conversion of product to reactant become equal and constant. The reversible reaction is an example of dynamic equilibrium.

Answer to Problem 100E

The statement, “The essential feature of a dynamic equilibrium is that the rates of opposing changes are equal” is true.

Explanation of Solution

In dynamic equilibrium the rate of forward and backward reaction is equal and constant. The formation of product and the breakdown of product to reactant take place at the same rate. Therefore, the rates of opposing changes are equal in dynamic equilibrium.

Conclusion

The statement, “The essential feature of a dynamic equilibrium is that the rates of opposing changes are equal” is true.

Interpretation Introduction

(i)

Interpretation:

Whether the statement, “Equilibrium vapor pressure depends on the concentration of a vapor above its own liquid” is true or false is to be identified.

Concept introduction:

The process of conversion of particles of a substance from a liquid state to gaseous state below the boiling point of the substance is known as evaporation. At a temperature lower than the boiling point of a liquid, the particles are in equilibrium with liquid state and gaseous state. The particles in the gas state exert vapor pressure.

Answer to Problem 100E

The statement, “Equilibrium vapor pressure depends on the concentration of a vapor above its own liquid” is true.

Explanation of Solution

The pressure exerted by the vapors of the liquid is known as vapor pressure. The strength of vapor pressure is determined by the concentration of vapors present over a liquid. Therefore, equilibrium vapor pressure depends on the concentration of a vapor above its own liquid.

Conclusion

The statement, “Equilibrium vapor pressure depends on the concentration of a vapor above its own liquid” is true.

Interpretation Introduction

(j)

Interpretation:

Whether the statement, “The heat of vaporization is equal to the heat of fusion, but with opposite sign” is true or false is to be identified.

Concept introduction:

The process of conversion of particles of a substance from a liquid state to gaseous state below the boiling point of the substance is known as evaporation. At a temperature lower than the boiling point of a liquid, the particles are in equilibrium with liquid state and gaseous state. The particles in the gas state exert vapor pressure.

Answer to Problem 100E

The statement, “The heat of vaporization is equal to the heat of fusion, but with opposite sign” is false.

Explanation of Solution

The amount of heat required to change the state from solid to liquid is known as heat of fusion. Whereas, the amount of heat required to change the state from liquid to gas is known as heat of vaporization. Therefore, heat of fusion and heat of vaporization is not equal.

Conclusion

The statement, “The heat of vaporization is equal to the heat of fusion, but with opposite sign” is false.

Interpretation Introduction

(k)

Interpretation:

Whether the statement, “The boiling point of a liquid is a fixed property of the liquid” is true or false is to be identified.

Concept introduction:

The process of conversion of particles of a substance from a liquid state to gaseous state below the boiling point of the substance is known as evaporation. At a temperature lower than the boiling point of a liquid, the particles are in equilibrium with liquid state and gaseous state. The particles in the gas state exert vapor pressure.

Answer to Problem 100E

The statement, “The boiling point of a liquid is a fixed property of the liquid” is false.

Explanation of Solution

The temperature at which vapor pressure of a liquid becomes equal to the atmospheric pressure is known as boiling point. However, the boiling point of a liquid varies with the atmospheric pressure. Therefore, the boiling point of a liquid is not a fixed property of the liquid.

Conclusion

The statement, “The boiling point of a liquid is a fixed property of the liquid” is false.

Interpretation Introduction

(l)

Interpretation:

Whether the statement, “If you break (shatter) an amorphous solid, it will break in straight lines, but if you break a crystalline solid, it will break in curved lines” is true or false is to be identified.

Concept introduction:

Amorphous and crystalline are the two types of solid. They differ from each other on the basis of their particle arrangement. Particles are arranged in regular and random manner in crystalline and amorphous solids, respectively.

Answer to Problem 100E

The statement, “If you break (shatter) an amorphous solid, it will break in straight lines, but if you break a crystalline solid, it will break in curved lines” is false.

Explanation of Solution

Amorphous and crystalline are the two types of solid. They differ from each other on the basis of their particle arrangement. Particles are arranged in regular and random manner in crystalline and amorphous solids, respectively. Amorphous solid give curved lines on shattering whereas crystalline solid give straight lines.

Conclusion

The statement, “If you break (shatter) an amorphous solid, it will break in straight lines, but if you break a crystalline solid, it will break in curved lines” is false.

Interpretation Introduction

(m)

Interpretation:

Whether the statement, “Ionic crystals are seldom soluble in water” is true or false is to be identified.

Concept introduction:

The solubility of two substances depends on “like dissolves like” principle that means polar substances dissolve in polar solvents and non-polar substances will dissolve in non-polar solvents.

Answer to Problem 100E

The statement, “Ionic crystals are seldom soluble in water” is false.

Explanation of Solution

Ionic crystals are made up of cations and anions. When ionic crystal is added into water, it gives respective ions and dissolves. Therefore, ionic crystals are readily soluble in water.

Conclusion

The statement, “Ionic crystals are seldom soluble in water” is false.

Interpretation Introduction

(n)

Interpretation:

Whether the statement, “Molecular crystals are nearly always soluble in water” is true or false is to be identified.

Concept introduction:

A bond formed between two atoms by transfer of electrons or by sharing of electrons is known as chemical bond. The chemical bonds are responsible for holding together atoms in a molecule, ions in ionic compounds and atoms in metals.

Answer to Problem 100E

The statement, “Molecular crystals are nearly always soluble in water” is false.

Explanation of Solution

Molecular crystals are made up of atoms which are bonded to each other by covalent bond. Covalent bond between atoms does not break when molecular crystal is added into water. Therefore, molecular crystals are insoluble in water.

Conclusion

The statement, “Molecular crystals are nearly always soluble in water” is false.

Interpretation Introduction

(o)

Interpretation:

Whether the statement, “The numerical value of heat of vaporization is always larger than the numerical value of heat of condensation” is true or false is to be identified.

Concept introduction:

The amount of energy required to change the state of a substance is known as enthalpy. It is the different in the energy of final and initial state of a substance. The negative and positive sign of enthalpy indicates the energy released and energy absorbed, respectively, during the phase change.

Answer to Problem 100E

The statement, “The numerical value of heat of vaporization is always larger than the numerical value of heat of condensation” is false.

Explanation of Solution

Vaporization and condensation are the opposite processes. Vaporization is converting liquid to gas and condensation is converting gas to liquid. The numerical value of heat of vaporization and heat of condensation has same value but opposite sign.

Conclusion

The statement, “The numerical value of heat of vaporization is always larger than the numerical value of heat of condensation” is false.

Interpretation Introduction

(p)

Interpretation:

Whether the statement, “The units of heat of fusion are $\text{kJ}/\text{g}\cdot °\text{C}$” is true or false is to be identified.

Concept introduction:

The amount of energy required to change the state of a substance is known as enthalpy. It is the different in the energy of final and initial state of a substance. The negative and positive sign of enthalpy indicates the energy released and energy absorbed, respectively, during the phase change.

Answer to Problem 100E

The statement, “The units of heat of fusion are $\text{kJ}/\text{g}\cdot °\text{C}$” is false.

Explanation of Solution

The amount of heat required to change the state from solid to liquid is known as heat of fusion. The units of heat of fusion is $\text{kJ}$.

Conclusion

The statement, “The units of heat of fusion are $\text{kJ}/\text{g}\cdot °\text{C}$” is false.

Interpretation Introduction

(q)

Interpretation:

Whether the statement, “The temperature of water drops while it is freezing” is true or false is to be identified.

Concept introduction:

The amount of energy required to change the state of a substance is known as enthalpy. It is the different in the energy of final and initial state of a substance. The negative and positive sign of enthalpy indicates the energy released and energy absorbed, respectively, during the phase change.

Answer to Problem 100E

The statement, “The temperature of water drops while it is freezing” is false.

Explanation of Solution

The temperature during the phase transformation remains constant. When water is freezing, the temperature does not increase or decrease. It remains constant.

Conclusion

The statement, “The temperature of water drops while it is freezing” is false.

Interpretation Introduction

(r)

Interpretation:

Whether the statement, “Specific heat is concerned with a change in temperature” is true or false is to be identified.

Concept introduction:

The amount of energy required to change the state of a substance is known as enthalpy. It is the different in the energy of final and initial state of a substance. The negative and positive sign of enthalpy indicates the energy released and energy absorbed, respectively, during the phase change.

Answer to Problem 100E

The statement, “Specific heat is concerned with a change in temperature” is true.

Explanation of Solution

The specific heat of a molecule is defined as the heat required to increase the temperature of the substance by $1°\text{C}$. Therefore, specific heat is concerned with a change in temperature.

Conclusion

The statement, “Specific heat is concerned with a change in temperature” is true.