STUDY GUIDE THERMOCHEMISTRY Q M C T H

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Study Guide Review of Gases

Study Guide Thermochemistry


Q = m C T H = -q C = 4.184 J

moles g oC


  1. When 150-g sample of KCl dissolves in 65.0 g of water in a calorimeter, the temperature drops from 31.0°C to 20.5°C. Calculate ΔH for the process. Use q = mCt

KCl(s) K+(aq) + Cl-(aq) ΔH=?


q = (65.0 g)(4.184 J)(-10.5oC)

g oC


q = -2855.58 J


150 g x 1 mole KCl = 2.012 moles

74.55 g


H = 2855.58 J = 1.42 kJ Endothermic

2.012 mole moles


  1. When a 12.0-g sample of NaI dissolves in 90.0 g of water in a calorimeter, the temperature rises from 20.5°C to 29.5°C. Calculate ΔH for the process.

NaI(s) Na+(aq) + I-(aq) ΔH=?


q = (90.0 g)(4.184 J)(9oC)

g oC


q = 3389.04 J


12.0 g x 1 mole NaI = 0.08 moles

149.9 g


H = -3389.04 J = -42.3 k J Exothermic

0.08 mole moles


  1. When a 25.8-g sample of NaOH dissolves in 45.0 g of water in a calorimeter, the temperature rises from 25°C to 90°C. Calculate ΔH for the process.

NaOH(s) Na+(aq) + OH-(aq) ΔH=?


q = (45.0 g)(4.184 J)(65oC)

g oC


q = 12238.2 J


25.8 g x 1 mole NaOH = 0.645 moles

40 g


H = -12238.2 J = -18.974 kJ Exothermic

0.645 mole moles


  1. When a 35.5-g sample of KCN dissolves in 140 g of water in a calorimeter, the temperature drops from 30°C to 14°C. Calculate ΔH for the process.

KCN(s) K+(aq) + CN-(aq) ΔH=?


q = (140 g)(4.184 J)(-16oC)

g oC


q = -9372.16 J


35.5 g x 1 mole KCN = 0.5453 moles

65.1 g


H = 9372.16 J = 17.2 kJ Endothermic

0.5453 mole moles


  1. When a 15 g sample of SrCl2 dissolves in 80 g of water in a calorimeter, the temperature drops from 42 oC to 15 oC . Calculate the H for the process. Use q = mCt

SrCl2(s) Sr+(aq) + 2 Cl-(aq)


q = (80 g)(4.184 J)(-27oC)

g oC


q = -9037.44 J


15 g x 1 mole SrCl2 = 0.0946 moles

158.52 g


H = 9037.44 J = 95.5 k J Endothermic

0.0946 mole moles


  1. When 35-g sample of KI dissolves in 180 g of water in a calorimeter, the temperature drops from 45°C to 18°C. Calculate ΔH for the process.

KI(s) K+(aq) + I-(aq) ΔH=?


q = (180 g)(4.184 J)(-27oC)

g oC


q = -20334.24 J


35 g x 1 mole KI = 0.2108 moles

166 g


H = 20334.24 J = 96.5 kJ Endothermic

0.2108 mole moles


  1. What is the specific heat of aluminum if the temperature of a 54.6-g sample of aluminum is increased by 15.7°C when 300 J of heat is added?


C = 300 J = 0.3499 J

(54.6 g)(15.7°C) g °C


  1. What is the specific heat of silicon if the temperature of a 27.99-g sample of silicon is increased by 24°C when 642 J of heat is added?


C = 642 J = 0.956 J

(27.99 g)(24°C) g °C


  1. What is the specific heat of gold if the temperature of a 79.5-g sample of gold is increased by 45°C when 460 J of heat is added?


C = 460 J = 0.129 J

(79.5 g)(45°C) g °C


  1. What is the specific heat of silver if the temperature of a 107.6-g sample of silver is increased by 90°C when 6590 J of heat is added?


C = 6590 J = 0.68 J

(107.6 g)(90°C) g °C


  1. What is the specific heat of titanium if the temperature of a 487-g sample of titanium is increased by 5.6°C when 1970 J of heat is added?


C = 1970 J = 0.722 J

(487 g)(5.6°C) g °C


  1. What is the specific heat of lead if the temperature of a 150 g sample of lead is increased by 39 oC when 607J of heat is added?


C = 607 J = 0.104 J

(150 g)(39°C) g °C


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