Week 6 - Thermodynamics (fundamental functions of thermodynamics) Flashcards
What is the difference between thermodynamics and thermochemistry?
- Thermodynamics, the study of energy and its transformations.
- Thermochemistry, branch of thermodynamics, deals with the heat involved in chemical and physical changes.
- When energy is transferred from one object to another, it appears as work and/or heat
The System and its Surroundings
First clearly define both the system and its surroundings
System + Surroundings = Universe
- The internal energy, E, of a system is the sum of the potential and kinetic energies of all the particles present.
- The total energy of the universe remains constant.
- A change in the energy of the system must be accompanied by an equal and opposite change in the energy of the surroundings.
Transfer of Internal Energy (E) Between a System and its Surroundings
ΔE = Efinal − Einitial = Eproducts − Ereactants
Energy will either be released to the surroundings (making ΔE -ve), or absorbed from surroundings (making ΔE +ve).
Heat and Work: Two Forms of Energy Transfer
- Heat (q) is the energy transferred as a result of…
Work (w) is the energy transferred when…
The total change in a system’s internal energy is the sum of the energy transferred as heat and/or work: (Equation)
the difference in temperature between the system and surroundings.
an object is moved by a force.
ΔE = q + w
The first law of Thermodynamics
The first law of Thermodynamics states that the total energy
of the universe is constant.
* Energy is conserved and is neither created nor destroyed.
Energy is transferred in the form of heat and/or work.
* ΔEuniverse = ΔEsystem + ΔEsurroundings = 0.
The total energy of a system is called…
The total energy of a system is called its internal energy, U.
The internal energy is a state function and only depends on the current state of the system.
A change in the internal energy (ΔU = Ufinal – Uinitial) is path independent.
The internal energy can be changed by the two processes work and heat:
ΔU = w + q
The internal energy of an isolated system is constant
Pressure-volume work is done when…
what is work of expansion?
what is work of contraction?
the volume of the system changes in the presence of an external pressure, P.
(w = – P. delta V)
- Work of expansion: the volume of the system increases if the temp is raised or if a chemical reaction results in a net increase in no. moles of gas. The system expands and has work done by the system on the surroundings, losing energy.
- Work of contraction: the volume of the system decreases if the temperature is lowered or if a chemical reaction results in a net decrease in the number of moles of gas. The system contracts and has work done on it by the surroundings, gaining energy as work.
Expansion work
Equation:
𝑑𝑤 = −𝑝𝑒𝑥𝑡𝑒𝑟𝑛𝑎𝑙.dV
To obtain the total work done when the volume changes from an initial value Vi to a final value Vf
it is necessary to integrate this expression between the initial and final volumes:
𝑤 = − integral (between 𝑉𝑓 and 𝑉𝑖) 𝑝𝑒𝑥𝑡𝑒𝑟𝑛𝑎𝑙.dV
Expansion work
Expansion against constant pressure: (equation)
𝑤 = −𝑝𝑒𝑥𝑡𝑒𝑟𝑛𝑎𝑙.∆V
Expansion against a constant pressure is an irreversible process.
Where should you look for a table of equations on different types of work (Expansion, Surface expansion, Extension and Electrical)?
Qmplus, Chemistry, week 6
Heat at constant volume
If heat is exchanged while keeping the volume of a system constant, then
dw = ? and ΔU = ?
dw = 0
ΔU = qV
Constant-Volume Calorimetry:
what is it carried out in?
what is it used to measure?
what is known about the calorimeter?
-carried out in a bomb calorimeter
-used to measure heat of combustion - this device measures the heat released at constant volume (qV
).
-The heat capacity, C, of the entire calorimeter is known.
* qcalorimeter = ccalorimeter × masscalorimeter × ΔTcalorimeter
q = c × m × ΔT
* q = heat lost or gained.
* c = specific heat capacity.
* m = mass in g.
* ΔT = Tfinal – Tinitial.
simplifies to
qcalorimeter = Ccalorimeter × ΔTcalorimeter
The specific heat capacity (c) of a substance is …
the quantity of heat required to change the temperature of 1 gram of the substance by 1 K.
The heat capacity at constant volume is denoted CV
and is defined formally as 𝐶v = ?
𝐶v = (𝜕𝑈 / 𝜕𝑇)v
Heat capacities are extensive properties: 100 g of water, for instance, has 100 times the heat capacity of 1 g of water.
Enthalpy: Chemical Change at Constant Pressure
What is Enthalpy defined (equation):
Enthalpy (H) is defined as E + PV so,
- ΔH = ΔE + PΔV Or ΔH = ΔU + PΔV
If a system remains at constant pressure and its volume does not change much, then,
* ΔH ≈ ΔE.
