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Chapter 5: Q43 E (page 271)

Calculate the enthalpy of solution (∆H for the dissolution) per mole of CaCl2(refer to Exercise 5.25).

Short Answer

Expert verified

The enthalpy of a solution (∆H for the dissolution) per mole of CaCl2 is 81 kJ/mol.

Step by step solution

01

Given data

The molar mass of CaCl2 = 110.98 g/mol.

Mass of CaCl2 = 3.0g.

\begin{aligned}{\rm{NumberofmolesofCaC}}{{\rm{l}}_{\rm{2}}}{\rm{=}}\frac{{{\rm{givenmass\;}}}}{{{\rm{molarmass}}}}{\rm{\;\;\;\;\;\;\;\;\;\;\;\;\;\;\;\;\;\;\;\;\;\;\;\;\;\;\;\;\;\;\;\;\;\;\;\;\;\;\;\;\;\;\;\;\;\;\;\;\;\;\;\;\;\;\;\;\;\;\;\;}}\\{\rm{=}}\frac{{{\rm{3}}{\rm{.0g}}}}{{{\rm{110}}{\rm{.98g/mol}}}}{\rm{\;\;\;\;\;\;\;\;\;\;\;\;\;\;\;\;\;\;\;\;\;\;\;\;\;\;\;\;\;\;\;\;\;\;\;\;\;\;\;\;\;\;\;\;\;\;\;\;\;\;\;\;\;\;\;\;\;\;\;\;\;\;}}\\\end{aligned}

\begin{aligned}{\rm{=0}}{\rm{.0270 mol}}\end{aligned}

02

Enthalpy of a solution

The formula for finding the enthalpy of a solution is given below:

\[{\bf{Enthalpy=}}\frac{{{\bf{Heat of the solution}}}}{{{\bf{Number of moles}}}}\]

The known values are substituted:

\begin{aligned}{\rm{Enthalpy=}}\frac{{{\rm{2}}{\rm{.2kJ}}}}{{{\rm{0}}{\rm{.0270mol}}}}{\rm{\;}}\\{\rm{=81kJ/mol}}\end{aligned}

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Most popular questions from this chapter

Water gas, a mixture of \({{\bf{H}}_{\bf{2}}}\) and CO, is an important industrial fuel produced by the reaction of steam with red hot coke, essentially pure carbon:\({\bf{C}}\left( {\bf{s}} \right){\bf{ + }}{{\bf{H}}_{\bf{2}}}{\bf{O}}\left( {\bf{g}} \right) \to {\bf{CO}}\left( {\bf{g}} \right){\bf{ + }}{{\bf{H}}_{\bf{2}}}\left( {\bf{g}} \right)\).

(a) Assuming that coke has the same enthalpy of formation as graphite, calculate \({\bf{\Delta H}}_{{\bf{298}}}^{\bf{0}}\)for this reaction.

(b) Methanol, a liquid fuel that could possibly replace gasoline, can be prepared from water gas and additional hydrogen at high temperature and pressure in the presence of a suitable catalyst:\({\bf{2}}{{\bf{H}}_{\bf{2}}}\left( {\bf{g}} \right){\bf{ + CO}}\left( {\bf{g}} \right) \to {\bf{C}}{{\bf{H}}_{\bf{3}}}{\bf{OH}}\left( {\bf{g}} \right)\).

Under the conditions of the reaction, methanol forms as a gas. Calculate \({\bf{\Delta H}}_{{\bf{298}}}^{\bf{0}}\)for this reaction and for the condensation of gaseous methanol to liquid methanol.

(c) Calculate the heat of combustion of 1 mole of liquid methanol to H2O(g) and CO2(g).

How many kilojoules of heat will be released when exactly 1 mole of iron, Fe, is burned to form Fe2O3(s) at standard state conditions?

Question: If 14.5 kJ of heat were added to 485 g of liquid water, how much would its temperature increase?

Ethanol, \({{\bf{C}}_{\bf{2}}}{{\bf{H}}_{\bf{5}}}{\bf{OH}}\), is used as a fuel for motor vehicles, particularly in Brazil.

(a) Write the balanced equation for the combustion of ethanol to CO2(g) and H2O(g), and, using the data in Appendix G, calculate the enthalpy of combustion of 1 mole of ethanol.

(b) The density of ethanol is 0.7893 g/ml. Calculate the enthalpy of combustion of exactly 1 L of ethanol.

(c) Assuming that an automobile’s mileage is directly proportional to the heat of combustion of the fuel, calculate how much farther an automobile could be expected to travel on 1 L of gasoline than on 1 L of ethanol. Assume that gasoline has the heat of combustion and the density of n–octane, \({{\bf{C}}_{\bf{8}}}{{\bf{H}}_{{\bf{18}}}}\) (ΔHf=

- 208.4 kJ/mol; density = 0.7025 g/mL).

A 92.9-g piece of a silver/gray metal is heated to 178.0 °C, and then quickly transferred into 75.0 mL of water initially at 24.0 °C. After 5 minutes, both the metal and the water have reached the same temperature: 29.7 °C. Determine the specific heat and the identity of the metal. (Note: You should find that the specific heat is close to that of two different metals. Explain how you can confidently determine the identity of the metal).
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