Molar Heat Calculations and Comparing Fuels

Module 1: Lesson 5 ASSIGNMENT

(12 marks)
Lesson 5 Assignment

Part 1: Molar Heat Calculations

(3 marks)
1.
Calculate the molar enthalpy of the NaOH(aq) using the data obtained from this experiment. Show all your work.

Answer:

Specific heat capacity: 4.19 J/g∙°C
50.0 ml of 1.0 mol/L NAOH
Initial temperature: 23.9 °C
Final temperature: 32.9 °C
Change in temperature: 9 °C

Q = mc∆t = (80g)(4.19 J/g∙°C)(9°C) = 3016.8 J or 3.0168 kJ

∆­­­­­­­­rH = n∆­­­­­­­­rH­m­
3.0168 kJ = (0.05 mol) (∆­­­­­­­­rH­m­­)
∆­­­­­­­­rH­m­ ­= 60 kJ/mol

(2 marks)
2.
The accepted molar enthalpy of neutralization of sodium hydroxide is - 57 kJ/mol. Calculate the % difference of the value you obtained from your experiment with this accepted value.

Answer:
% difference = | accepted – experimental| x 100 accepted

= |57 – 60.336| x 100 -57 = 5.85%

(7 marks)
Part 2: Try This—Comparing Fuels

The table below displays information about different types of fuels that can be used at a campsite for cooking. Examine the information in the table.

a) For each fuel, determine the energy content per gram (kJ/g) and record this value in the table below.(2 marks)

b) Based on the information in the table, which fuel would be most suitable for the purposes of camping? Justify your fuel choice by making reference to energy content per gram and the other data provided in the table. You will be assessed based on how well you support your opinion. (5 marks)

Fuel
Kerosene
Ethanol
Methanol
Wood
Propane
Biogas (Methane)
State
(l)
(l)
(l)
(s)
(g)
(g)
ΔcHm (kJ/mol)
- 8.33 x 103
- 1.37 x 103
- 728
-2.51 x 103
-2.22 x 103
-891
Molar mass (g/mol)
Approx 110 – 226
46.08
32.05
Assume cellulose (C6H10O5)n , 162.16)
44.11
16.05
Energy Content (kJ/g)
Average of 110 and 226 = 168

Energy content = - 49.6
-29.7
-22.7
-15.5

-50.3
-55.5
Toxicity
Poisonous

Poisonous

Poisonous
Poisonous
Relative Stability
High
High