THERMOCHEMISTRY Flashcards
Kinetic energy
Energy associated with motion (thermal)
Potential energy
Energy associated with position (chemical)
Kinetic energy formula
KE = 1/2mv^2
System
Set of substances and energy being studied
Surroundings
Everything else not part of the system
3 types of system
- Open system: Exchange of energy and matter
- Closed system: Exchange of energy
- Isolated system: No exchange
First law of thermodynamics
States that energy can neither be created or destroyed, only altered in form
Internal energy
Sum of potential and kinetic energy (Delta U = q + w)
Heat (q)
Transfer of thermal energy between system and surroundings caused by temperature difference
Thermal equlibrium
Occurs when heat transfer stops
+q
Absorbs heat (endothermic)
-q
Releases heat (exothermic)
What type of system is a calorimeter
Isolated
+w
On the system
-w
By the system
Chemical reactions in solution in a calorimeter
qrxn = -Csoln msoln DeltaTsoln
Chemical reactions not in solution
qrxn = -Ccal mcal DeltaTcal
Relationship between system and surroundings
Inversely proportional. If system gains 300J, then surrounding loses 300J
Work (w)
Product of force and distance
Work formula
W = -P DeltaV OR -Deltan RT
State function
Property whose values dont depend on the pathway taken (internal energy)
Pathway function
Property whose values depend on the pathway taken (heat and work)
Bomb calorimeter
Constant volume (Delta V = 0)
Enthalpy (H)
Sum of internal energy PLUS pressure and volume (Delta H = Delta U + DeltaPV) or Delta H = a qrxn/nlimiting
+H
Absorbing energy (endothermic)
Systen <—- Surroundings
-H
Releasing energy (exothermic)
System —–> Surroundings
Hess’ law
States that the change in enthalpy is the same whether the reaction takes place in one or a series of steps
