Chapter 2- Review II Flashcards
What is heat?
The flow of energy caused by a temperature difference
What is the system and the surroundings?
The system is the object/solution being studied
The surroundings is anything with which the system can exchange energy
What is the first law of thermodynamics?
The total energy in the universe is constant
What is the internal energy?
What is it’s symbol?
Equation for finding change in internal energy?
How does it compare form a system to its surroundings
The sum of the kinetic and potential energies of all the particles that compose a system
E or ΔΕ
ΔE=q + w
Esys = -Esurr
When is heat, work and internal energy positive?
Heat (q)- when system gains thermal energy
Work (w)- when work is done on the system
ΔE- when energy flows into the system
What is the heat capacity?
Specific heat capacity?
Molar heat capacity?
Heat capacity- heat required to change temp by 1 degree C
Specific- heat required to change temp by 1 degree C of 1 gram of substance
Molar- heat required to change temp by 1 degree C of 1 mole of the substance
What is the formula for finding heat using heat capacity and change in temp?
How about for a bomb calorimeter?
Q = C (ΔT)
Or
q= m x Cs x ΔT
Bomb
Qcal = Ccal x ΔT
How does the heat of the surroundings differ from the heat of the system?
qsys = -qsurr C(ΔT)sys= -C(ΔT)surr
What is the formula for work?
What’s re the signs when gas expands?
W= -PΔV
ΔV= + W= - when gas expands
What is the internal energy equation for heat at a constant volume?
ΔErxn = qv
Qv= heat at constant volume
How does the heat from a calorimeter compare to the heat of the reaction?
How do you find the internal energy of the reaction when you have moles and qcal?
Qcal = qsurr = -qrxn
Qrxn= nΔErxn
Then ΔErxn = qrxn/n
What is enthalpy and its formula?
What is the formula with heat at a constant pressure?
The sum of the internal energy and the product of its pressure and volume
ΔH=ΔE+PΔV
Constant pressure
ΔΗ=(qp+w) + (-w)
ΔΗ= qp (heat at constant pressure)
How does enthalpy represent exothermic and endothermic reactions?
ΔH= -
Heat is being released by system, exothermic
ΔΗ= +
Heat is being absorbed by the system, Endothermic
What do we use to measure ΔHrxn?
What is the formula?
Coffee cup calorimeter
Qsoln=msoln x Cssoln x ΔT
qrxn=-qsoln=-qcal
What is the standard state for gas, liquid of solid, and substance in a solution?
Gas- pure gas at 1 atm
Liquid of solid- pure substance in most stable form at 1 atm and temperature of interest (often 25C)
substance in solution- concentration of 1M
What is the standard enthalpy change?
Change in enthalpy for a process when all reactants and products are in their standard states
ΔH*
(degree)
What is the standard enthalpy of formation for a pure compound and a pure element in its standard state?
Pure compound- change in enthalpy when 1 mole of compound forms from the elements in their standard states
Pure element- ΔH*f = 0
What does volatile mean?
Liquids that vaporize easily
What is the heat of vaporization?
Its symbol?
Amount of heat required to vaporize one mole of liquid to gas
ΔHvap
Always positive since vaporization is endothermic
What is vapor pressure?
The pressure of a gas in dynamic equilibrium with its liquid
What is the boiling point and the normal boiling point of a liquid?
Boiling point- the temperature at which its vapor pressure equals the external pressure
Normal boiling point- the temperature at which its vapor pressure equals 1atm
What is the heat of fusion?
The amount of heat required to melt 1 mole of a solid
ΔHfus is positive since melting is endothermic
What is ΔHsub equal too?
ΔHsublimation= ΔHvaporization + ΔHfusion
Also is equal to -ΔHdeposition
What is -ΔHdeposition equal to?
-ΔHdeposition = -ΔHcondensation + (-ΔHfreezing)
What is Clausius-Clapeyron equation involving change in pressure, change in temp, R, -ΔHvaporization, and ln?
ln(P2/P1) = -ΔHvaporization/R
(1/T2 - 1/T1)
Use antilog if you need to find pressure
What is exothermic vs endothermic?
Exo-releases heat, raises temp of surroundings
dE is negative
Endo- absorbs heat, cools surroundings
dE is positive
