Chapter 5 Flashcards
(34 cards)
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
