Foothill High School • Chemistry
Ch 17
Q = mcp∆T
Cp values in J/g·K
H2O(l) – 4.18
Al(s) – 0.897
Water – ∆Hfus = 334 J/g
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Thermochemistry WS #4
1kg = 1000g; 1kJ = 1000J; 1 cal = 4.184 J
H2O(s) – 2.06
Fe(s) – 0.449 Cu(s) – 0.385
H2O(g) – 1.87
Cu (l) – 0.572
Ethanol (l) – 2.44
Au(s) 0.129
∆Hvap = 2260 J/g
1) Identify the following reactions as exothermic or endothermic (circle correct answer)
a. 2H2(g)+ O2(g) Æ 2H2O(g) ∆H = -571.6 kJ
b. FeS + 2HCl Æ H2S + FeCl2 ∆H = 4450KJ
c. CS2 + 3Cl2 + 176 kJ Æ CCl4 + S2Cl2
d. 2 Na(s) + 2 H2O(l) Æ 2 NaOH(aq) + H2 (g) + 367.5 kJ
endothermic
endothermic
endothermic
endothermic
exothermic
exothermic
exothermic
exothermic
2) How much energy, in calories, is removed when cooling 200.0 g of water from 100°C to 25°C?
3) How much energy, kilojoules, will it take to heat 1550 grams of ice from –70°C to room temperature
(25°C)?
4) How much energy does it take to heat 500.0 g of gold from –20°C to 75°C? The melting temperature of
gold is 1064°C and the heat of fusion is 12.55 kJ/mol.
5) An unknown piece of metal with a mass of 50.0g is heated from 22.0°C to 98.2°C. To reach this
temperature it absorbed 1.71 kJ of energy. What is the most likely identity of this metal?
6) The melting point of copper is 1358K and the boiling point is 2835K. How much energy is needed to
completely melt 5.00 kg of copper that starts at 20.0°C? (∆Hfus = 209 J/g; ∆Hvap = 4.72 kJ/g)
7) (challenge question) The combustion of methane is shown by the following equation
CH4(g) + O2(g) Æ CO2(g) + H2O(g)
∆H = -802 kJ/mol
If you had 0.580 grams of methane at STP, what is the maximum temperature a 52.0 g piece of copper could
reach if it started at 25°C (assume all the heat from the reaction goes to heat the copper)?