Chapter U5, Problem C18.4RE

(a)

Interpretation Introduction

Interpretation:

The direction of energy transferred in the process of conversion of water to ice is to be discussed.

Concept introduction:

Whenever the state of a substance changes, a transfer of heat takes place.

Conversion of solid to liquid or liquid to gas requires heat and gas to liquid or liquid to solid releases heat.

Answer to Problem C18.4RE

Energy is transferred from water to the freezer.

Explanation of Solution

When the water is in a liquid form in the freezer, it is converted to ice which is a solid form. A fixed amount of energy is released when liquid is converted to solid. So, there is a transfer of energy from water to the freezer.

(b)

Interpretation Introduction

Interpretation:

The energy transferred in the process of conversion of water to ice is whether endothermic or exothermic for ice tray is to be discussed.

Concept introduction:

Whenever the state of a substance changes, a transfer of heat takes place.

Conversion of solid to liquid or liquid to gas requires heat and gas to liquid or liquid to solid releases heat.

A process is endothermic when there is an absorption of heat and exothermic when there is a release of heat.

Answer to Problem C18.4RE

The process is exothermic for the ice tray.

Explanation of Solution

When the water is in a liquid form in the freezer, it is converted to ice which is a solid form. A fixed amount of energy is released when liquid is converted to solid. So, there is a transfer of energy from water to the freezer. So, the process is exothermic by virtue of tray.

(c)

Interpretation Introduction

Interpretation:

The amount of heat transferred for one ice cube is to be calculated.

Concept introduction:

Whenever the state of a substance changes, a transfer of heat takes place.

Conversion of solid to liquid or liquid to gas requires heat and gas to liquid or liquid to solid releases heat.

A process is endothermic when there is an absorption of heat and exothermic when there is a release of heat.

The amount of heat released when 1 mol of water freezes is called enthalpy of freezing.

Answer to Problem C18.4RE

Amount of heat released $=\text{8.33}kJ$

Explanation of Solution

The heat released when 1 mol water freezes $=\text{6}kJ$

  $\text{1}molwater=\text{18}g$

Density of water= $\text{1}g/mL$

Therefore,

  $volumeofwater=\text{18}mL$

Thus,heat released when $\text{18}mL$ water freezes $=\text{6}kJ$

So, heat released when $\text{25}mL$ water will freeze $=\frac{\text{6}}{\text{18}}\times \text{25}$

                   $=\text{8.33}kJ$

(d)

Interpretation Introduction

Interpretation:

The amount of heat transferred for full ice tray is to be calculated.

Concept introduction:

Whenever the state of a substance changes, a transfer of heat takes place.

Conversion of solid to liquid or liquid to gas requires heat and gas to liquid or liquid to solid releases heat.

A process is endothermic when there is an absorption of heat and exothermic when there is a release of heat.

The amount of heat released when 1 mol of water freezes is called enthalpy of freezing.

Answer to Problem C18.4RE

Amount of heat released $=\text{133.3}kJ$ .

Explanation of Solution

The heat released when 1 mol water freezes $=\text{6}kJ$

  $\text{1}molwater=\text{18}g$

Density of water= $\text{1}g/mL$

Therefore,

  $volumeofwater=\text{18}mL$

Thus,heat released when $\text{18}mL$ water freezes $=\text{6}kJ$

So, heat released when $\text{25}mL$ water will freeze $=\frac{\text{6}}{\text{18}}\times \text{25}$

                   $=\text{8.33}kJ$

Number of moulds in ice tray $=\text{16}$

Therefore,

Heat released when full tray is frozen $=\text{16}\times \text{8.33}$

               $=\text{133.33}kJ$