1. The specific heat of iron metal is 0.450 J/gK. How many J of heat are necessa
ID: 926812 • Letter: 1
Question
1. The specific heat of iron metal is 0.450 J/gK. How many J of heat are necessary to raise the temperature of a 1.05 kg block of iron from 28.0 Cto 85.0 C?
2. A 1.80-g sample of phenol (C6H5OH) was burned in a bomb calorimeter whose total heat capacity is 11.66 kJ/C. The temperature of the calorimeter plus contents increased from 21.36Cto 26.37C.
A. Write a balanced chemical equation for the bomb calorimeter reaction.
B. What is the heat of combustion per gram of phenol?
C. Per mole of phenol?
3. When a 9.55-g sample of solid sodium hydroxide dissolves in 100.0 g of water in a coffee-cup calorimeter, the temperature rises from 23.6 C to 47.4 C.
A. Calculate H (in kJ/mol NaOH) for the solution process NaOH(s)Na+(aq)+OH(aq). Assume that the specific heat of the solution is the same as that of pure water.
Explanation / Answer
1) we know that
heat = mass x specific heat x temp change
so
Q = m x s x dT
Q = 1.05 x 1000 x 0.45 x ( 85-28)
Q = 26932 J
so
26932 J of heat is required
2) the balanced reaction is
C6H5OH + 7 02 ----> 6 C02 + 3H20
B) heat absorbed by the calorimeter = heat capacity x temp change
Q = 11.66 x ( 26.37 - 21.36)
Q = 58.4166 kJ
now
heat of combustion per gram of phenol = heat / mass of phenol
= 58.4166 / 1.8
= 32.453 kJ / g
C) now
moles = mass / molar mass
so
moles of phenol = 1.8 / 94 = 0.019
now
heat of combustion per mole of phenol = 58.4166 / 0.019
heat of combustion per mole of phenol = 3050.644 kJ
3)
total mass = 109.55 g
now
heat = mass x specific heat x temp change
so
heat = 109.55 x 4.184 x ( 47.4 - 23.6)
heat = 10908.9 J
now
moles = mass / molar mass
so
moles of NaOH = 9.55/ 40 = 0.23875
now
dH = heat / moles of NaOH
dH = 10908.9 / 0.23875
dH = 45691 J/mol
dH = 45.691 kJ /mol
so
dH for the process is -45.691 kJ/mol
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