Chapter 5 Flashcards
Thermodynamics
study of heat, work, energy and the changes they produce in the states of systems
Thermochemistry
Branch of thermodynamics, the study of heat changes in chemical reactions
Heat
(q) a form of energy transfer that can occur when there is a temp. difference between the system and its surroundings. an extensive property
Work
(w) a form of energy transfer that occurs when a macroscopic force acts between the system and its surroundings. an extensive property
Types of macroscopic energy
- kinetic: due to motion of an object
- Potential: due to position/arrangement
3 Mechanical energy
Internal energy
a state function, the sum of all the kinetic and potential energies in a system
Law of conservation of energy
Energy can not be created or destroyed, it can be converted from one form
to another
Thermal energy
Kinetic energy of atoms, ions and molecules
Pressure
Force per area. P=F/A, intensive property
System
The part of the universe that is the focus of a thermodynamic study
Surroundings
Parts of the universe that can interact with the system
Types of systems
Isolated: Does not interact with surroundings
Closed: Energy but not matter can be transferred with surroundings
Open: Both energy and matter can be transferred with surroundingd
Exothermic
energy flows out of system to surroundings, q<0
Endothermic process
energy flows into system from surroundings, q>0
Work formula and types
w=Fd, types of work are electrical, magnetic, nuclear and chemical
How can you find 🔼E without initial/final values?
🔼E=q+w in a closed system only
Calorie
Amount of heat necessary to raise the temperature of 1 g of water by 1C
Joule
SI unit of energy
First law of thermodynamics
The total energy of the system and surroundings is conserved
🔼TE(sys)+🔼TE(surr)=0
In what situation does TE=E
system is at rest(KE=0) and there are no external fields(PE=0)
PV work(including 🔼V, Vfinal, Vinitial and W in each situation)
work associated with compression or expansion
compression: Work is done on the system. w>0, 🔼V<0, Vfinal(Vinitial, w=-P🔼V>0
Expansion: Work done by the system
w<0, 🔼V>0, Vfinal>Vinitial
W=-P🔼V<0
Enthalpy
(H) A state function and extensive property, it is the sum of internal energy and PV product of a system.
H=E+PV
🔼H
Closed system and constant P when only the PV work is allowed: 🔼H=Qp
Qp= Heat exchanged at constant pressure
Constant pressure: 🔼H=🔼E+P🔼V
Constant volume: 🔼H=🔼E+V🔼P
General change of state: 🔼H=🔼E+🔼(PV)
H and 🔼H in endothermic and exothermic reactions
Endothermic: 🔼H>0, Hproducts>Hreactants
Exothermic: 🔼H<0, Hproducts
Molar heat capacity
c(p) Quantity of energy required to raise the temperature of 1 mole of a substance by 1C
q=n•c(p)•🔼T
Specific heat
(Cs) The energy required to raise the temperature of 1 gram of a substance by 1C at constant P
q=m•Cs•🔼T
Heat capacity
(Cp) quantity of energy needed to raise the temperature of an object by 1C(at constant P)
Molar enthalpy of fusion
(🔼Hfus) the energy required to convert 1 mole of a solid at its melting point into a liquid state
q=n•🔼Hfus
Molar enthalpy of vaporization
(🔼Hvap) The energy required to convert 1 mole of a liquid at its boiling point to the vapor state
Bomb calorimeter
A constant volume device used to measure energy released during a combustion reaction. Heat produced in reaction=heat gained by calorimeter
Standard molar enthalpy of formation
enthalpy change for reaction in which one mole of a substance is formed from elements in their standard states(1 bar, usually 298K/25C)
Fuel value
The energy released during complete combustion of 1g of a substance
Fuel density
The energy released during complete combustion of 1L of a liquid fuel
Food value
The quantity of energy produced when a material consumed by an organism for sustenance is burned completely, determined by bomb calorimetry
