Exam (elaborations)

Sustainable Energy 1st Edition By Richard Dunlap - Test Bank

0 purchase

Course
Sustainable Energy Test Bank

Institution
Sustainable Energy Test Bank

Chapter 3 Fossil Fuel Resources and Use 3.1 A person's primary energy needs are supplied exclusively by burning oil (with an energy content of 3.85 × 107 J/L). If a person's average power consumption is 12 kW, how long would it take that person to use one barrel of oil (158.97 liters)? So...

[Show more]

Preview 4 out of 78 pages

View example

Uploaded on August 29, 2023
Number of pages 78
Written in 2022/2023
Type Exam (elaborations)
Contains Questions & answers

complete test bank
all chapters included
sustainable energy 1st edition by richard dunlap

Institution
Sustainable Energy Test Bank
Education
Sustainable Energy Test Bank
Course
Sustainable Energy Test Bank

ExamsExpert

Member since 1 year 454 documents sold

R440,37

Add to cart

Add to wishlist

100% satisfaction guarantee
Immediately available after payment
Both online and in PDF
No strings attached

, Sustainable Energy - Chapter 1: Energy Basics

Chapter 1
Energy Basics

1.1 One liter of water is cubic meter of water is poured off a 50 m high tower every
second. If the change in gravitational potential energy is converted into electricity with an
efficiency of 86%, how many 60 W light bulbs can be illuminated?

Solution Potential energy is

.

One liter of water has a mass of 1 kg, so for a height difference of 50 m, the corresponding
energy is

E = (1 kg) × (9.8 m/s2) × (50 m) = 490 J.

If this energy is converted into electricity with an efficiency of 85% then the electrical
energy available will be (590 J) × (0.85) = 421 J. If this amount of energy is produced
every second then the corresponding power is

P = (421 J)/(1 s) = 421 W.

This will illuminate

(421 W)/(60 W) = 7 light bulbs.

1.2 A beam of light is comprised of photons with energy 2.1 eV. What is the wavelength of
the light?

Solution A photon's energy is related to frequency by

Frequency is related to the wavelength λ by

so that

1
©2015 Cengage Learning. All Rights Reserved. May not be scanned, copied or duplicated, or posted to a publicly accessible website, in whole or in part.

,Sustainable Energy - Chapter 1: Energy Basics

Solving for wavelength gives

For an energy of 2.1 eV, the corresponding wavelength is

1.3 A boiler produces steam at 520°C and this steam is used to run a heat engine to
produce mechanical energy. It is desired to use a river as the cold heat reservoir and to
have a Carnot efficiency of 45%. Is this feasible?

Solution Converting to degrees K gives

520°C + 273 = 793 K.

The Carnot efficiency is given by

η = 100 × (1 – Tc/Th)

solving for Tc gives

Tc = Th(1 – η/100)

In order to have a Carnot efficiency of 45% when Th = 793 K requires

Tc = (793 k) × (1 – 0.45) = 436 K = 163°C.

Well within the possibilities of using a river as the cold reservoir.

1.4 Octane produces energy according to the reaction

2C8H18 + 25O2 → 16CO2 + 18H2O + 44.4 MJ/kg.

If an automobile burns octane and requires 3.0 MJ of thermal energy from combustion to
travel 1 km. How many moles of octane need to be burned for a trip of 100 km?

Solution At 3.0 MJ/km, a trip of 100 km will require 300 MJ of thermal energy from
combustion. As 1 kg of octane produces 44.4 MJ of energy, then to produce 300 MJ will
require

(300 MJ)/(44.4 MJ/kg) = 6.76 kg of octane.

2
©2015 Cengage Learning. All Rights Reserved. May not be scanned, copied or duplicated, or posted to a publicly accessible website, in whole or in part

, Sustainable Energy - Chapter 1: Energy Basics

The molecular mass of octane C8H18 is (8 × 12) + (18 × 1) = 114 g/mol or 0.114 kg/mol.
Thus 6.76 kg will consist of

(6.76 kg)/(0.114 kg/mol) = 59.3 mol

1.5 Ethanol (heat of combustion 28.9 MJ/kg) is burned to produce heat and that heat is
used to raise the temperature of water. How many kg of ethanol will be needed to raise the
temperature of 1 m3 of water from 20°C to its boiling point (but not to convert the liquid to
vapor)?

Solution The energy required to heat an object is given by

E = mcΔT

where m is the mass, c is the specific heat and ΔT is the change in temperature. 1 m 3 of
water will have a mass of 1000 kg and the specific heat of water is 4180 J/(kg°C). So
substituting in the above expression gives the energy required as

E = (1000 kg) × (4180 J/(kg°C) × (100ºC – 20 ºC) = 334 MJ.

For ethanol with a heat of combustion of 28.9 MJ/kg the required heat corresponds to an
ethanol mass of

(334 MJ)/(28.9 MJ/kg) = 11.6 kg.

1.6 A heat pump is used to heat a house. The outside temperature is –5°C and the inside
temperature is +21°C. What is the coefficient of performance of the heat pump?

Solution The temperatures must be converted to Kelvin as

–5°C + 273 = 268 K
+21°C + 273 = 294 K

The coefficient of performance may then be calculated to be

COP = 1/(1 – Tc/Th)) = [1 – (268 K)/(294 K)]–1 = 11.3

3
©2015 Cengage Learning. All Rights Reserved. May not be scanned, copied or duplicated, or posted to a publicly accessible website, in whole or in part.

The benefits of buying summaries with Stuvia:

Guaranteed quality through customer reviews

Stuvia customers have reviewed more than 700,000 summaries. This how you know that you are buying the best documents.

Quick and easy check-out

You can quickly pay through EFT, credit card or Stuvia-credit for the summaries. There is no membership needed.

Focus on what matters

Your fellow students write the study notes themselves, which is why the documents are always reliable and up-to-date. This ensures you quickly get to the core!

Frequently asked questions

What do I get when I buy this document?

You get a PDF, available immediately after your purchase. The purchased document is accessible anytime, anywhere and indefinitely through your profile.

Satisfaction guarantee: how does it work?

Our satisfaction guarantee ensures that you always find a study document that suits you well. You fill out a form, and our customer service team takes care of the rest.

Who am I buying this summary from?

Stuvia is a marketplace, so you are not buying this document from us, but from seller ExamsExpert. Stuvia facilitates payment to the seller.

Will I be stuck with a subscription?

No, you only buy this summary for R440,37. You're not tied to anything after your purchase.

Can Stuvia be trusted?

4.6 stars on Google & Trustpilot (+1000 reviews)

68175 documents were sold in the last 30 days

Founded in 2010, the go-to place to buy summaries for 15 years now

Start selling

Exam (elaborations)

Sustainable Energy 1st Edition By Richard Dunlap - Test Bank

Document information

Subjects

Written for

Seller

Reviews received

Content preview