Thermochemistry Problems With Answers printable pdf download

Thermochemistry Problems With Answers

CHAPTER 5: ANSWERS TO ASSIGNED PROBLEMS

Hauser- General Chemistry I

revised 10/14/08

CAUTION: Many different units are used in thermochemistry. Report the units!

Also report the sign when appropriate!

5.41 Consider the following reaction:

2 Mg (s) + O

(g)  2 MgO (s) ΔH = -1204 kJ

(a) Is this reaction exothermic or endothermic?

EXOTHERMIC (negative ΔH)

(b) Calculate the amount of heat transferred when 2.4 g of Mg (s) reacts at constant

pressure.

2.4 g Mg ( 1 mol Mg / 24.31 g) ( -1204 kJ / 2 mol Mg) = -59 kJ (2 SF)

COEFFICIENTS MATTER! Note the 2 for Mg.

5.43 When solutions containing silver ions and chloride ions are mixed, silver chloride

precipitates:

(aq) + Cl

(aq)  AgCl (s) ΔH = -65.5 kJ

(a) Calculate ΔH for production of 0.200 mol of AgCl by this reaction.

0.200 mol AgCl ( -65.5 kJ / 1 mol AgCl) = -13.1 kJ

(b) Calculate ΔH for the production of 2.50 g of AgCl.

Ag 1 X 107.87

Cl 1 X 35.45

sum = 143.32

2.50 g AgCl ( 1 mole AgCl / 143.32 g ) ( -65.5 kJ / 1 mole AgCl ) = - 1.14 kJ

Thermochemistry Problems With Answers