# Written assignment 7: energy and thermochemistry

Written Assignment 7: Energy and Thermochemistry
Answer all assigned questions and problems, and show all work.
1. Consider this reaction:
2CH3OH(l) + 3O2(g) → 4H2O(l) + 2CO2(g) ∆H = –1452.8 kJ/mol
a. Is this reaction endothermic or exothermic? (2 points)
b. What is the value of ∆H if the equation is multiplied throughout by 2? (2 points)
c. What is the value of ∆H if the direction of the reaction is reversed so that the products become the reactants and vice versa? (2 points)
d. What is the value of ∆H if water vapor instead of liquid water is formed as the product? (2 points)
(Reference: Chang 6.24)
2. The first step in the industrial recovery of zinc from the zinc sulfide ore is roasting,
that is, the conversion of ZnS to ZnO by heating:
2ZnS(s) + 3O2(g) → 3ZnO(s) + 2SO2(g)  ∆H = –879 kJ/mol
Calculate the heat evolved (in kJ) per gram of ZnS roasted. (5 points)
(Reference: Chang 6.25)
3. A 6.22 kg piece of copper metal is heated from 20.5 °C to 324.3 °C. Calculate the heat absorbed (in kilojoules) by the metal. Specific heat Cu = 0.385 J/g°C. (5 points)
(Reference: Chang 6.33)
4. A sheet of gold weighing 10.0 g and at a temperature of 18.0 °C is placed flat on a sheet of iron weighing 20.0 g and at a temperature of 55.6 °C. What is the final temperature of the combined metals? Assume that no heat is lost to the surroundings. (5 points) (Reference: Chang 6.35)
5. A 0.1375 g sample of solid magnesium is burned in a constant-volume bomb calorimeter that has a heat capacity of 3024 J/°C. The temperature increases by 1.126°C. Calculate the heat given off by the burning Mg, in kJ/g and in kJ/mol. (5 points)
(Reference: Chang 6.37)
6. Calculate the heat of decomposition for this process at constant pressure and 25°C: (10 points)
CaCO3(s)  → CaO(s) + CO2(g)
(Reference: Chang 6.51)
7. Methanol, ethanol, and n-propanol are three common alcohols. When 1.00 g of each of these alcohols is burned in air, heat is liberated as shown by the following data: (a) methanol (CH3OH), –22.6 kJ/g; (b) ethanol (C2H5OH), –29.7 kJ/g; (c) n-propanol (C3H7OH), –33.4 kJ/g. Calculate the heats of combustion of these alcohols in kJ/mol.(12 points)
a) Methanol
b) Ethanol
c) n-propanol (C3H7OH), –33.4 kJ/g
(Reference: Chang 6.55)
8. From the standard enthalpies of formation, calculate ΔH°rxn for the reaction
C6H12(l) + 9O2(g) → 6CO2(g)  + 6H2O(l)
For C6H12(l), ΔH°f = –151.9 kJ/mol (5 points)
(Reference: Chang 6.57)
9. Determine the amount of heat (in kJ) given off when 1.26 × 104 g of ammonia are produced according to the equation
N2(g) + 3H2(g) → 2NH3(g)  ΔH°= –92.6 kJ/mol
Assume that the reaction takes place under standard conditions at 25oC. (5 points)
(Reference: Chang 6.59)
10. From the following heats of combustion,
CH3OH(l) + 3/2O2(g) → CO2(g) + 2H2O(l) ΔHorxn = –726.4 kJ/mol
C(graphite) + O2(g)  → CO2(g)   ΔHorxn = –393.5 kJ/mol
H2(g) + ½O2(g) → H2O(l)   ΔHorxn = –285.8 kJ/mol
Calculate the enthalpy of formation of methanol (CH3OH) from its elements.
C(graphite) + 2H2(g) + ½O2(g) → CH3OH(l) (10 points)
(Reference: Chang 6.63)
11. Methanol (CH3OH) is an organic solvent and is also used as a fuel in some automobile engines. From the following data, calculate the standard enthalpy of formation of methanol:   (5 points)
(Reference: Chang 6.87)
12. A 44.0 g sample of unknown metal at 99.0 °C was placed in a constant-pressure calorimeter, with a heat capacity of 12.4 J/°C, containing 80.0 g of water at 24.0°C. The final temperature of the system was found to be 28.4 °C. Calculate the specific heat of the metal. (10 points)
(Reference: Chang 6.85)
13. A person ate 0.50 pound of cheese (an energy intake of 4000 kJ). Suppose that none of the energy was stored in his body. What mass (in grams) of water would he need to perspire in order to maintain his original temperature? (It takes 44.0 kJ to vaporize 1 mole of water.)   (5 points)
14. The total volume of the Pacific Ocean is estimated to be 7.2 × 108 km3. A medium-sized atomic bomb produces 1.0 × 1015 J of energy upon explosion. Calculate the number of atomic bombs needed to release enough energy to raise the temperature of the water in the Pacific Ocean by 1°C. (10 points)

Calculate the price
Pages (550 words)
\$0.00
*Price with a welcome 15% discount applied.
Pro tip: If you want to save more money and pay the lowest price, you need to set a more extended deadline.
We know how difficult it is to be a student these days. That's why our prices are one of the most affordable on the market, and there are no hidden fees.

Instead, we offer bonuses, discounts, and free services to make your experience outstanding.
How it works
Receive a 100% original paper that will pass Turnitin from a top essay writing service
step 1
Fill out the order form and provide paper details. You can even attach screenshots or add additional instructions later. If something is not clear or missing, the writer will contact you for clarification.
Pro service tips
How to get the most out of your experience with Australia Assessments
One writer throughout the entire course
If you like the writer, you can hire them again. Just copy & paste their ID on the order form ("Preferred Writer's ID" field). This way, your vocabulary will be uniform, and the writer will be aware of your needs.
The same paper from different writers
You can order essay or any other work from two different writers to choose the best one or give another version to a friend. This can be done through the add-on "Same paper from another writer."
Copy of sources used by the writer
Our college essay writers work with ScienceDirect and other databases. They can send you articles or materials used in PDF or through screenshots. Just tick the "Copy of sources" field on the order form.
Testimonials
See why 20k+ students have chosen us as their sole writing assistance provider
Check out the latest reviews and opinions submitted by real customers worldwide and make an informed decision.
Nursing
Customer 453627, January 23rd, 2020
Education
Thank you!
Customer 463875, April 29th, 2023
Psychology
I received a 91 on the quiz, which is still a good gade.
Customer 452455, April 5th, 2023
SEO
A job well done
Customer 463679, May 9th, 2023
Good one
Customer 452615, July 16th, 2022
Military
excellent paper
Customer 456821, January 14th, 2023
History
The work was really good and done on time.
Customer 454439, June 1st, 2020
Organization behavior
thank you
Customer 462271, November 30th, 2021
Political science
Great job God bless you
Customer 453983, February 4th, 2020
Health Care
Thank you so much!
Customer 454001, March 8th, 2020
Economics
I would like to thank you for your hard work. The essay is clear and clean.
Customer 462687, March 14th, 2022
Education
Always proofread before submitting to eliminate minor errors.
Customer 462495, April 3rd, 2022
11,595
Customer reviews in total
96%
Current satisfaction rate
3 pages
Average paper length
37%
Customers referred by a friend