* Your assessment is very important for improving the workof artificial intelligence, which forms the content of this project
Download Energy
Survey
Document related concepts
International Energy Agency wikipedia , lookup
Cogeneration wikipedia , lookup
Zero-energy building wikipedia , lookup
Energy efficiency in transport wikipedia , lookup
Low-carbon economy wikipedia , lookup
Energy returned on energy invested wikipedia , lookup
Compressed air energy storage wikipedia , lookup
Alternative energy wikipedia , lookup
Negawatt power wikipedia , lookup
Energy policy of the European Union wikipedia , lookup
Environmental impact of electricity generation wikipedia , lookup
Energy Independence and Security Act of 2007 wikipedia , lookup
Internal energy wikipedia , lookup
Micro combined heat and power wikipedia , lookup
Gibbs free energy wikipedia , lookup
Transcript
Introductory Chemistry: A Foundation, 6th Ed. Introductory Chemistry, 6th Ed. Basic Chemistry, 6th Ed. by Steven S. Zumdahl & Donald J. DeCoste University of Illinois Chapter 10 Energy Energy and Energy Changes • Energy: ability to do work or produce heat – Chemical, mechanical, thermal, electrical, radiant, sound, nuclear – Potential and kinetic • Energy may affect matter. – e.g. Raise its temperature, eventually causing a state change, or cause a chemical change such as decomposition • All physical changes and chemical changes involve energy changes. Copyright © Houghton Mifflin Company. All rights reserved. 10 | 3 Energy and Energy Changes • Potential Energy: energy due to composition or position • Kinetic Energy: energy due to motion – - ½ mv2 Copyright © Houghton Mifflin Company. All rights reserved. 10 | 4 Energy and Energy Changes (cont.) • Law of Conservation of Energy: energy can be converted from one form to another, but cannot be created or destroyed Copyright © Houghton Mifflin Company. All rights reserved. 10 | 5 Work and Energy • Work: force acting over a distance – w=f•d – Work done on a system will increase the energy of the system, whereas work done by the system will decrease the energy of the system • State function: a property that changes independent of pathway Copyright © Houghton Mifflin Company. All rights reserved. 10 | 6 Temperature and Heat • Heat: a flow of energy due to a temperature difference • Temperature: a measure of the random motions of the components of a substance Copyright © Houghton Mifflin Company. All rights reserved. 10 | 7 Temperature and Heat (cont.) Copyright © Houghton Mifflin Company. All rights reserved. 10 | 8 Exothermic vs. Endothermic • System: that part of the universe that we wish to study • Surroundings: everything else in the universe • Exothermic process: a process that results in the evolution of heat - Example: when a match is struck, it is an exothermic process because energy is produced as heat. • Endothermic process: absorbs heat - Example: melting ice to form liquid water is an endothermic process because the ice absorbs heat in order to melt Copyright © Houghton Mifflin Company. All rights reserved. 10 | 9 Exothermic Process Copyright © Houghton Mifflin Company. All rights reserved. 10 | 10 Thermodynamics • The Law of Conservation of Energy is also known as The First Law of Thermodynamics. It can be stated as “the energy of the universe is constant.” • Internal Energy (E) = kinetic energy + potential energy • ∆E = q + w = change in internal energy q = heat absorbed by the system w = work done on the system Copyright © Houghton Mifflin Company. All rights reserved. 10 | 11 Units of Energy • One calorie = amount of energy needed to raise the temperature of one gram of water by 1°C – kcal = energy needed to raise the temperature of 1000 g of water 1°C • joule – 4.184 J = 1 cal • In nutrition, calories are capitalized. – 1 Cal = 1 kcal Copyright © Houghton Mifflin Company. All rights reserved. 10 | 12 Example - Converting Calories to Joules Convert 60.1 cal to joules. 1 cal = 4.184 joules 4.184 J 60.1cal × = 251J 1 cal Copyright © Houghton Mifflin Company. All rights reserved. 10 | 13 Energy & Temperature of Matter • The amount the temperature of an object increases depends on the amount of heat added (q). – If you double the added heat energy the temperature will increase twice as much. • The amount the temperature of an object increases when heat is added depends on its mass – If you double the mass it will take twice as much heat energy to raise the temperature the same amount. Copyright © Houghton Mifflin Company. All rights reserved. 10 | 14 Specific Heat Capacity • Specific heat (s): the amount of energy required to raise the temperature of one gram of a substance by one degree Celsius J By definition , the specific heat of water is 4.184 g °C Amount of Heat = Specific Heat x Mass x Temperature Change Q = s x m x ∆T Copyright © Houghton Mifflin Company. All rights reserved. 10 | 15 Specific Heat Capacity Copyright © Houghton Mifflin Company. All rights reserved. 10 | 16 Example #1: Calculate the amount of heat energy (in joules) needed to raise the temperature of 7.40 g of water from 29.0°C to 46.0°C. Copyright © Houghton Mifflin Company. All rights reserved. 10 | 17 Example #1 (cont.) Specific heat of water = 4.184 J g°C Mass = 7.40 g Temperature change = 46.0°C – 29.0°C = 17.0°C Q = s • m • ∆T J Heat = 4.184 × 7.40g ×17.0°C = 526 J g °C Copyright © Houghton Mifflin Company. All rights reserved. 10 | 18 Example #2 A 1.6 g sample of metal that appears to be gold requires 5.8 J to raise the temperature from 23°C to 41°C. Is the metal pure gold? Copyright © Houghton Mifflin Company. All rights reserved. 10 | 19 Example #2 Q = s × m × ∆T Q s= m × ∆T ∆T = 41°C - 23°C = 18°C 5.8 J J s= = 0.20 1.6 g x 18°C g °C Table 10.1 lists the specific heat of gold as 0.13 Therefore the metal cannot be pure gold. Copyright © Houghton Mifflin Company. All rights reserved. J g °C 10 | 20 Enthalpy • Change in enthalpy (∆Hp = qp): the amount of heat exchanged when heat exchange occurs under conditions of constant pressure • Enthalpy is a state function • ∆H is independent of the path taken Copyright © Houghton Mifflin Company. All rights reserved. 10 | 21 Hess’s Law • Hess’s Law: in going from a set of reactants to a set of products, the change in enthalpy is the same whether the reaction takes place in one step or in a series of steps. Copyright © Houghton Mifflin Company. All rights reserved. 10 | 22 Hess’ Law (cont.) • ∆Hreaction= ∑∆hsteps • If the direction of a reaction is reversed, the sign of ∆H is reversed. • ∆Hforward = -∆hreverse • Magnitude of ∆H α quantities of reactants and products Copyright © Houghton Mifflin Company. All rights reserved. 10 | 23 Hess’s Law (cont.) • Overall reaction: N2 + 2O2 2NO2 ∆H = 68 kJ • This reaction can be carried out in 2 steps: N2 + O2 2NO ∆H = 180 kJ 2NO + O2 2NO2 ∆H = -112 kJ -------------------------------------------------------N2 + 2O2 2NO2 ∆H = 68 Kj Note: the sum of the two reactions gives the overall reaction and the same is true for the sum of the enthalpy change values. Copyright © Houghton Mifflin Company. All rights reserved. 10 | 24 Calorimetry • The amount of heat flow transferred during a reaction is determined from temperature measurements made in a calorimeter. Copyright © Houghton Mifflin Company. All rights reserved. 10 | 25 Calorimetry (cont.) Copyright © Houghton Mifflin Company. All rights reserved. 10 | 26 Energy Quality & Quantity • While the total amount or quantity of energy in the universe is constant (1st Law) the quality of energy is degraded as it is used. Burning of petroleum: High grade concentrated energy energy (heat) Copyright © Houghton Mifflin Company. All rights reserved. Low grade 10 | 27 Fuels • Petroleum – A fossil fuel composed mainly of hydrocarbons • Natural gas – Consists largely of methane – Also contains ethane, propane, and butane Copyright © Houghton Mifflin Company. All rights reserved. 10 | 28 Fuels (cont.) Copyright © Houghton Mifflin Company. All rights reserved. 10 | 29 Fuels (cont.) Copyright © Houghton Mifflin Company. All rights reserved. 10 | 30 Fuels (cont.) • Coal – Matures geologically through stages Copyright © Houghton Mifflin Company. All rights reserved. 10 | 31 Global Warming Copyright © Houghton Mifflin Company. All rights reserved. 10 | 32 Global Warming (cont.) Copyright © Houghton Mifflin Company. All rights reserved. 10 | 33 Energy Use and Sources Copyright © Houghton Mifflin Company. All rights reserved. 10 | 34 Energy as a Driving Force • Most processes that occur spontaneously involve an “energy spread.” – Heat flows from high to low temperature and “spreads” …or a “matter spread” – Salt dissolves or “spreads” in water Copyright © Houghton Mifflin Company. All rights reserved. 10 | 35 Entropy • Entropy (S) is a measure of disorder or randomness. – As a system becomes more disordered, ∆S >0 • Second Law of Thermodynamics: the entropy of the universe is always increasing. Copyright © Houghton Mifflin Company. All rights reserved. 10 | 36