Question

1. The specific heat of iron metal is 0.450 J/g⋅K. 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 21.36∘Cto 26.37∘C.

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 ΔH (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.

Answer 1

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