Thermodynamics Flashcards
What is internal energy?
The sum of all kinetic and potential energies of all components in the system
DE = E final - E initial
(change in internal energy)
What if the change in internal energy is >0 or <0
> 0 = then final is greater than initial. The system has absorbed energy from surroundings - energy change is endergonic
<0 = system released energy to surroundings so energy change is exergonic.
What is the total change in internal energy equal to?
Total change in internal energy = q + w
q= heat
w= work
what is endothermic?
Heat absorbed by the system from the surroundings - DH is positive
What is exothermic?
Het released from system to surroundings - DH is negative
Define internal energy
a state function
what is work?
When a process occurs in an open container, the only work done is a change in volume of a gas pushing on the surroundings
W = -p DV
p= pressure in Pa
DV - change in volume
what is enthalpy ?
if a process takes place at a constant pressure & the only work done is the pressure-volume work, we can account for heat flow during the process by measuring enthalpy change
H = E + PV Enthalpy = internal energy + product of pressure and volume
what is DH equal tO?
DH = q
Change in enthalpy equation
DH = H products - H reactants
How can we measure changes in heat for the system (enthalpy change)?
constant pressure calorimetry - aqueous solution, indirectly mesure heat change by measuring what change for water
Bomb calorimetry - measure heat absorbed by water- measure change in internal energy
what is Hess law?
if a reaction is carried out in a series of steps, Enthalpy change for the overall reaction will be equal to the sum of the enthalpy changes for the individual steps
Define enthalpy change of formation
enthalpy change for reaction in which a compound is made from its constituent elements in their elemental forms
Measured under standard conditions 298K, 1 atm
How is calorimetry used to measure change in enthalpy?
Measure heat flow
The change in sample will be felt by the water, heat is transferred to water if it reacts and the thermometer will read it.
Define heat capacity
amount of energy required to raise the temperature of a substance by 1K
