Chap 9: thermochemistry Flashcards
A calorie
Energy requird to raise 1g of water by 1degrees
1 Calorie = 4.184J
Internal energy, KE, PE, and total energy
Energy stored in form of chemical bonds, molecular translations, rotations and vibrations.
KE is the energy of motion
PE is the energy of interaction with external fields like gravity.
Total Energy = Internal energy + PE + KE
When a system loses energy, the surrounds gain that.
First law of thermodynamics, isolated system
Change in E of sys + Change in E of surr = 0.
An isolated system does not interact with sorr. Energy of an isolated system is cons (the entire universe is an isolated system)
For a system at rest, and no external fields of interaction, change in internal energy is?
= Heat(q) + work(w)
difference btn heat and temperature
Heat means energy transfer from one system to another (same as work)
temperature is the measure of energy.
State functions (Energy), heat, and work.
Energy is a state property so one can say that a system has a certain amount of energy associated with its state. (it does not depend on the process)
Heat and work are not state functions, they are process dependent. Just like distance is “route” dependent.
Therefore, one should not say that a system has a certain amount of heat and work.
One cannot define change in heat or work.
Why is sand hotter than water in the beach
- sand has a lower heat capacity
Thermal equilibrium
When two specimens with diff temperatures are placed in thermal contact, they will eventually reach thermal equilibrium.
if T2 > T1, heat flows from 2 to 1.
The magnitude of heat lost by specimen 2 = magnitude of heat absorbed by specimen 1.
Constant volume process
Heat is not a state function, however, if transferred at a constant volume, then the amount of heat does represent a change in state property.
Hess’s law
If two or more chemical reactions are added to give a new reaction, then adding the H values of the corresponding reactions gives the H of the new reaction
