大学化学课件-国外原版教材-5

Copyright 1999, PRENTICE HALL
Chapter 5
20
Hess’s Law
In the above enthalpy diagram note that DH1 = DH2 + DH3
Copyright 1999, PRENTICE HALL Chapter 5 21
Enthalpies of Formation
Relating DE to Heat and Work
Copyright 1999, PRENTICE HALL
Chapter 5
9
First Law of Thermodynamics
Endothermic and Exothermic Processes
Endothermic: absorbs heat from the surroundings. Exothermic: transfers heat to the surroundings. An endothermic reaction feels cold. An exothermic reaction feels hot.
Copyright 1999, PRENTICE HALL
Chapter 5
10
First Law of Thermodynamics
State Functions
State function: depends only on the initial and final states of system, not on how the internal energy is used.
Copyright 1999, PRENTICE HALL Chapter 5 6
First Law of Thermodynamics
Relating DE to Heat and Work
Energy cannot be created or destroyed. Energy of (system + surroundings) is constant. Any energy transferred from a system must be transferred to the surroundings (and vice versa). From the first law of thermodynamics:
Copyright 1999, PRENTICE HALL Chapter 5 15
Calorimetry
Heat Capacity and Specific Heat
Copyright 1999, PRENTICE HALL
Chapter 5
16
Calorimetry
Constant-Pressure Calorimetry
From Physics: • Force is a push or pull on an object. • Work is the product of force applied to an object over a distance: w=Fd • Energy is the work done to move an object against a force. • Kinetic energy is the energy of motion:
1J
We sometimes use the calorie instead of the joule: 1 cal = 4.184 J (exactly) A nutritional Calorie: 1 Cal = 1000 cal = 1 kcal
Copyright 1999, PRENTICE HALL Chapter 5 4
when a system undergoes a physical or chemical change, the change in internal energy is given by the heat added to or absorbed by the system plus the work done on or by the system: DE = q + w
• If 1 mol of compound is formed from its constituent elements, then the enthalpy change for the reaction is called the enthalpy of formation, DHof . • Standard conditions (standard state): 1 atm and 25 oC (298 K). • Standard enthalpy, DHo, is the enthalpy measured when everything is in its standard state. • Standard enthalpy of formation: 1 mol of compound is formed from substances in their standard states. • If there is more than one state for a substance under standard conditions, the more stable one is used.
Copyright 1999, PRENTICE HALL
Chapter 5
3
The Nature of Energy
Energy Units
SI Unit for energy is the joule, J: E k 1 mv 2 1 2 kg 1 m/s 2 2 2 2 2 1 kg m / s
Copyright 1999, PRENTICE HALL
Chapter 5
7
First Law of Thermodynamics
Relating DE to Heat and Work
Copyright 1999, PRENTICE HALL
Chapter 5
8
First Law of Thermodynamics
Atmospheric pressure is constant! D H = qP qrxn = -qsoln = -(specific heat of solution) (grams of solution) DT.
Copyright 1999, PRENTICE HALL
Chapter 5
Copyright 1999, PRENTICE HALL
Chapter 5
18
Calorimetry
Bomb Calorimetry (Constant-Volume Calorimetry)
qrxn = -CcalorimeterT.
Copyright 1999, PRENTICE HALL
Chapter 5
Chapter 5
5
First Law of Thermodynamics
Internal Energy
• Internal Energy: total energy of a system. • Cannot measure absolute internal energy. • Change in internal energy, DE = Efinal Einitial
Thermochemistry
David P. White University of North Carolina, Wilmington
Chapter 5
Copyright 1999, PRENTICE HALL Chapter 5 1
The Nature of Energy
Kinetic and Potential Energy
Copyright 1999, PRENTICE HALL
Chapter 5
11
First Law of Thermodynamics
State Functions
Copyright 1999, PRENTICE HALL
Chapter 5
12
Enthalpy
Enthalpy, H: Heat transferred between the system and surroundings carried out under constant pressure. Can only measure the change in enthalpy: DH = Hfinal - Hinitial = qP
Copyright 1999, PRENTICE HALL Chapter 5 14
Calorimetry
Heat Capacity and Specific Heat
Calorimetry = measurement of heat flow. Calorimeter = apparatus that measures heat flow. Heat capacity = the amount of energy required to raise the temperature of an object (by one degree). Molar heat capacity = heat capacity of 1 molific heat capacity = heat capacity of 1 g of a substance. q = (specific heat) (grams of substance) T. Be careful of the sign of q.
2 1 Ek mv 2
Copyright 1999, PRENTICE HALL Chapter 5 2