Chapter 11, Problem 45E

(a)

Interpretation Introduction

Interpretation: The amount of heat required to convert $\text{42}\text{.0}\text{g}$ of ethanol at $35°\text{C}$ to vapor phase at $78°\text{C}$ should be determined.

Concept Introduction:The enthalpy change for the conversion of ethanol from $35°\text{C}$ to $78°\text{C}$ of liquid ethanol is calculated as,
$\Delta H_1=m\times c\times \Delta T$

Where,

• $\Delta H_1$is the enthalpy change for this process.
• $m$ is the mass of ethanol.
• $c$ is the specific heat of liquid ethanol.
• $\Delta T$ is the change in the temperature.

The number of moles of ethanol is calculated by the formula,

  $n=\frac{m}{M}$

Here,

• $n$ is the number of moles of ethanol.
• $m$ is the given mass of ethanol.
• $M$ is the molar mass of ethanol.

Enthalpy change is calculated as,

  $\Delta H_2=n\times \Delta H_{\text{vap}}$

Where,

• $\Delta H_2$ is the enthalpy change during this process.
• $n$ is the moles of ethanol.
• $\Delta H_{\text{vap}}$ is the enthalpy of vaporization of ethanol.

(b)

Interpretation Introduction

Interpretation: The amount of heat required to convert $\text{42}\text{.0}\text{g}$ of ethanol at $-155°\text{C}$ to vapor phase at $78°\text{C}$ should be determined.

Concept Introduction:The enthalpy change can be calculated as follows:

 $\Delta H_1=m\times c\times \Delta T$

Where,

• $\Delta H_1$ is the enthalpy change for this process.
• $m$ is the mass of ethanol.
• $c$ is the specific heat of liquid ethanol.
• $\Delta T$ is the change in the temperature.

The number of moles of ethanol is calculated by the formula,

$n=\frac{m}{M}$

Here,

• $n$ is the number of moles of ethanol.
• $m$ is the given mass of ethanol.
• $M$ is the molar mass of ethanol.

Enthalpy change is calculated as,

$\Delta H_2=n\times \Delta H_{\text{vap}}$

Where,

• $\Delta H_2$ is the enthalpy change during this process.
• $n$ is the moles of ethanol.
• $\Delta H_{\text{vap}}$ is the enthalpy of vaporization of ethanol.