Phase Change Calculation Worksheet
Some helpful data:
q = mC∆T
1kg = 1000g
1kJ = 1000J
Name ___________________________
Date ____________________ Per ____
1 cal = 4.184 J;
1000 cal = 1 Cal
q for a phase change = n ∆Hf (melting) or n ∆Hv (boiling)
Specific Heat Values (Cp)
Substance
H2 O (s)
H2 O (l)
H2 O (g)
Au
Phase Change Values
Water: ΔHf = 6.01 kJ/mol
Specific Heat
2.06 J/gºC
4.18 J/gºC
2.02 J/gºC
0.129 J/gºC
ΔHv = 40.7 kJ/mol
1. Identify the following reactions as exothermic or endothermic (circle correct answer)
a.
b.
c.
d.
2H2(g)+ O2(g)  2H2O(g) ΔH = -571.6 kJ
FeS + 2HCl  H2S + FeCl2 ΔH = 4450KJ
CS2 + 3Cl2 + 176 kJ  CCl4 + S2Cl2
2 Na(s) + 2 H2O(l)  2 NaOH(aq) + H2 (g) + 367.5 kJ
endothermic
endothermic
endothermic
endothermic
exothermic
exothermic
exothermic
exothermic
2. How much heat is required to boil 25.0g of Ethanol (C2H5OH) at 78.5ºC? (BP of ethanol is
78.5 ºC ; ΔHv = 43.5 kJ/mol)
3. How much heat is removed when condensing 25.0g of water at 100ºC?
4. How much heat (kJ) does it take to heat 200 grams of water from 25ºC to 100ºC?
5. How much energy, in calories, is removed when cooling 200.0 g of water from 100°C to
25°C?
6. How much energy does it take to heat a 500 g sample of gold from -20 ºC to 75ºC?
7. You have a sample of H2O with a mass of 23.0g at a temperature of -46.0ºC. How many
kilojoules of heat energy are necessary to:
a. Heat the ice to 0ºC?
b. Melt the ice?
c. Heat the water from 0ºC to 100ºC?
d. Boil the water?
e. Heat the steam from 100ºC to 109ºC?
8. The ΔHvap for water is 40.7 kJ/mol.
a. Show the conversion to J/g
b. Show the conversion to Cal/g