thermodynamic lecture 1

Question 1

what is work?

Answer 1

is the mode of transfer of energy that achieves or utilises uniform motion of matter in the surroundings

Question 2

what is heat ?

Answer 2

is the mode of transfer of energy that achieves or utilises disorderly motion in the surroundings

Question 3

what is The Thermodynamic Universe consist from ?

Answer 3

1- System = the part of the world in which we have an interest
2- Surroundings = the part of the world from which we observe the system; surroundings are assumed to be infinite, remain
at constant temperature, pressure, volume – no matter what
the system does
3-Universe = System + Surroundings

Question 4

what is open system?

Answer 4

can exchange energy and matter with the surroundings (changes in composition possible)

Question 5

what is close system ?

Answer 5

can exchange energy but not matter with its surroundings

Question 6

what is isolated system ?

Answer 6

can exchange neither energy nor matter with its surroundings

Question 7

example of Some spontaneous changes are not associated with any change of internal energy at all ?

Answer 7

for example the isothermal expansion of a perfect gas

No change in internal energy

Question 8

A non-spontaneous change always requires work ?

Answer 8

• A gas can be compressed
• A cool object can be heated up with electric current
• Water can be dissociated by electrolysis

Question 9

A non-spontaneous change always requires work such as ?

Answer 9

• A gas can be compressed
• A cool object can be heated up with electric current
• Water can be dissociated by electrolysis

Question 10

what is entropy

Answer 10

Entropy (S) is the function that permits us to predict whether a process is spontaneous or not.

Question 11

what is entropy ?

Answer 11

Entropy (S) is the function that permits us to predict whether a process is spontaneous or not.
+
During any spontaneous process, the entropy of the universe increases.

Question 12

Energy leaves system→w and q ______

Answer 12

negative

Question 13

Energy enters system→w and q ______

Answer 13

positive

Question 14

Expansion Work becomes zero when the external ex pressure (Pex) is zero.

Answer 14

The greater the external pressure the greater the work done by the
system for a given volume change

Question 15

When the external pressure exceeds the internal pressure then a
compression of the gas takes place, and w _______

Answer 15

becomes positive.

Question 16

Maximum work is obtained when the external pressure is only infinitesimally less than the pressure of the gas in the system at all stages of the expansion

Answer 16

= mechanical equilibrium)
-A system that remains in mechanical equilibrium with its surroundings at all stages of an expansion does maximum expansion work.

Question 17

when ideal gas occurs ?

Answer 17

Adjusting the external pressure to always match internal pressure leads to perfect gas behaviour

Question 18

what is Reversible Process ?

Answer 18

A reversible process can be reversed by an infinitesimally small variation of one variable (e.g., pressure).
+
reversible, isothermal expansion work of a perfect gas

Question 19

Area under p=nRT/V curve is ____

Answer 19

Reversible isothermal expansion work

reversible =give max work expansion

Question 20

Irreversible expansion work is always ________ in magnitude than the expansion work associated with the reversible process

Answer 20

lower

Question 21

why the heat capacity also depends on whether the sample is maintained at constant volume during heating, or at constant pressure. ?

Answer 21

For the pressure to remain constant the gas must expand. This means that the gas loses energy as expansion work to its surroundings. So additional heat is required to compensate the energy loss from expansion work.

Question 22

when you add heat to the system you get _____

Answer 22

negative in work

Question 23

what is the internal energy (U) ?

Answer 23

The energy contained in the system (J)

U=q+w

Question 24

When q=-w, U=0 ?

Answer 24

when the amount of heat add is the same goes out = the same in isolated system

Question 25

what is 1st law of thermodynamics

Answer 25

The internal energy of an isolated system is constant

Question 26

Heat q transferred to the system from the surroundings is positive.
Work w done by the system expanding against an external force is negative so
w = −pdV
so the first law will be :

Answer 26

ΔU = q + w

Question 27

Heat q transferred to the system from the surroundings is positive.
Work w done by the system expanding against an external force is negative so
w = −pdV
so the first law will be :

Answer 27

ΔU = q + w

Question 28

Heat q transferred to the system from the surroundings is positive.
Work w done by the system expanding against an external force is negative so
w = +pdV
so the first law will be :

Answer 28

ΔU = q - w

Question 29

When the volume of a system is constant then no work can be exchanged with the surroundings (w = 0). The internal energy change becomes. U = qV

Answer 29

at constant volume

Question 30

When the volume of a system is constant then no work can be exchanged with the surroundings (w = 0). The internal energy change becomes. U = qV(indicate at at constant volume)

Answer 30

at constant volume

Question 31

what is uses of bomb calorimeter ?

Answer 31

1-used to determined heat released in a solution
2- measure temperature rise for combustion of test material
3-Determine calorimeter constant (heat capacity) in kJ/°C

Question 32

what is Enthalpy ?

Answer 32

Most chemical reactions occur in vessels open to the atmosphere and under constant (atmospheric) pressure

Question 33

Example of Enthalpy ?

Answer 33

decomposition of carbonates produces CO2 gas that must push back the surrounding atmosphere

Question 34

At constant pressure, the enthalpy change is equal to the amount of heat exchanged.

Answer 34

dH= dq(p)

Question 35

How do (i) the internal energy and (ii) the enthalpy of a perfect gas change during an isothermal expansion? Why?

Answer 35

nternal Energy and the 1st Law
• We have seen that heat and work are just different ways of transferring energy into or out of a system. This is called the equivalence of heat and work, a principle first formulated by James Joule in the 19th century.
• The energy contained in the system is called the internal energy, U [unit: J].
• In practice we cannot measure the total internal energy of a sample, because it
includes all the energies of all sub-atomic particles, i.e., nuclei, electrons, etc.
• We can only measure changes in internal energy:
U = w + q
Isothermal expansion of a perfect gas:
q = −w
The internal energy of a sample of perfect gas at a given temperature is
U = 0 independent of the volume it occupies.
Isolated system: no exchange of heat or work with surroundings.Hence the internal energy cannot change. This leads to the 1st law of thermodynamics:
The internal energy of an isolated system is constant
H = U + (pV) pV = nRT
H = U + (nRT)
(ii) Definition of enthalpy:
Perfect gas law:
Hence:
n and T are constant during an isothermal expansion, so (nRT) = 0 Since U is also zero (see above) it follows that
H = 0 as well!