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...the capacity to do work
First Law of Thermodynamics states...
- Energy can be neither created nor destroyed, merely transferred into a different form:
- Conservation of Energy
System + Surroundings
- Part of the universe we are interested in...
- Solutions in a beaker
- Chemical reactor
- Electrochemical cell
Everything else in contact with the system, which can influence its state
Exchange of BOTH energy and matter with the surroundings
Exchange of energy BUT NOT matter with the surroundings
No exchange of energy and matter with the surroundings
...the transfer of energy causing motion against a force
- Work = Force X displacement
- Work = Pressure X change in volume
- Pressure = Force / Area
...the transfer of energy as a result of a temperature difference between the systems and surroundings
Q + means...
Q - means...
- Q + means heat IN (absorbed by system)
- Q - means head OUT (absorbed by surroundings)
W + means...
W - means...
- W + means work DONE ON (a system)
- W - means work DONE BY (a system)
We use a calorimeter...
- To measure heat changes
- It is a reaction vessel surrounded by a water bath containing a thermometer
Heat supplied Q =
- Q = mwater X Cwater X ΔT
- Where C=heat capacity
- Where m=mass
At constant pressure Q =...
At constant volume Q=...
- Where U = Internal energy
- ΔH = ΔU + PΔV
- Remember W=P X ΔV
The reaction enthalpy is...
The measured heat change for a reaction at atmospheric pressure
Enthalpy is a state function, which means that...
A change in enthalpy depends only on the difference between the starting state and the final state, not on the route taken
Hess' Law definition 1
The standard enthalpy (ΔHo) of a reaction is the sum of the standard enthalpies of the reactions into whcih the overall reaction may be divided, even if this division is artificial.
Hess' law definition 2
The enthalpy change accompanying a chemical change is independent of the route by which the chemical change occurs.