Thermodynamics Flashcards
Energy
The capacity to do work or to transfer heat
Two Types of Energy
Kinetic Energy and Potential Energy
Electrostatic Potential Energy
Caused by interactions between charged particles
Energy is used in order to…
Break bonds and overcome IMFS
Energy is released when bonds are formed
System
What we’re looking at, the reaction taken place
Surroundings
Everything else
Internal Energy
The total energy of the system
Change in energy
q (heat) + w is work
Change in H
enthalpy
energy change per mole of reaction
+ H = endothermic (unfavorable)
- H = exothermic (favorable)
Substances with lower potential energy are…
More stable
Temperature
Measure of average kinetic energy
Thermal Equilibrium
When both blocks are at the same temperature so they have the same average kinetic energy
No net transfer of heat
Calorimeter
Measures heat flow
Heat Capacity
Amount of heat required to raise an object’s temperature by 1 degree C
J/C or J/K
Molar Heat Capacity
Amount of heat required to raise 1 mol of substance 1 degree C
J/molC or J/molK
Specific Heat Capacity
Amount of heat needed to raise 1 gram of substance by 1 degree C
J/gC or J/gK
Specific Heat of water
4.184 J/gC
q=
CpMChange in T
qwater=
-qrxn
Phase Changes Formula
Use q=CpMT for temperature changes
Use heat of fusion or heat of vaporization times moles of substance for phase changes
Change of H=
qp/molrxn
State Function
Property of a system that depends only on the present state of the system NOT the path taken to reach that state
cE,cH,cS,cG
Bond Enthalpy
The energy required to break a bond in 1 mol of gaseous substance (kJ/mol)
Change in Hrxn=
Sum of Bond enthalpies of bonds broken-sum of Bond enthalpies of bonds formed
Heat of formation is…
The heat change associated with the formation of 1 mole of a substance from its component elements
Enthalpies of Formation for calculating overall heat of reaction
=Sum of heat of formation of products-sum of heat of formation of reactants
Hess’s Law
If a reaction is carried out in a series of steps, change of H for the overall reacting equals the summer of all the heat changes for the individual steps
How to use Hess’s Law
Manipulate steps of a reaction to get overall reacting and use these manipulations on the individual heats of reaction and then add them up to get the overall heat of reaction
