Laws ofLaws ofThermodynamics Thermodynamics

11Disusun Oleh :Disusun Oleh :

Ichwan Aryono, S.Pd.Ichwan Aryono, S.Pd.

First law of First law of thermodynamicsthermodynamicsFirst Law of thermodynamics states that :

Whenever heat Q is given to a system, a portion of heat is used to increase its internal energy in the amount of U, whereas the remaining leaves the system when the system performs a work W to its surroundings.

Mathematically, the first law of thermodynamics is formulated by :

Q = U + W

Q>0

Q<0

W>0 W<0

W positip jika sistem melakukan usaha

W negatip jika sistem dikenai usaha

Q positip Jika sistem menerima kalor

Q negatip jika sistem melepas kalor

Energi dalam U tidak terpengaruh oleh proses, yang dilihat adalah hanya pada keadaan awal dan keadaan akhir

The first law of thermodynamics for The first law of thermodynamics for isothermal processisothermal process

At isothermal Process : T = 0, so U = 0

The work done by the isothermal process is :

Q = U + W = 0 + W = W

Q =

1

2lnV

VnRTW

1

2lnV

VnRTW

The first law of thermodynamics for The first law of thermodynamics for isobaricisobaricprocessprocess

At isobaric process the pressure is constant

P = 0

Internal energy , so

)(2

5

2

52

3

12 VVPVPQ

VPVPWUQ

The first law of thermodynamics The first law of thermodynamics for for

isochoric processisochoric process

At Isochoric process volume is constant, V = 0, so the work done W = PV = 0, its produce :

)(2

3

2

3

0

12 TTnRTnRUQ

UWUQ

The first law of thermodynamics The first law of thermodynamics for adiabaticfor adiabatic

process processAdiabatic process is a process without any transfer of heat into or from the system (Q=0)and it applies :

)(2

3

)(2

3

0

21

12

TTnRW

TTnRUW

WU

WUQ

Student Activity #1Student Activity #1

A system absorbs 1500 J of heat from surrounding and does work done 2200 J . Determine the change of internal energy system, increases or decreases ?

Student ActivityStudent Activity

Mention three general variables of Mention three general variables of thermodynamicsthermodynamics

What is state function ?What is state function ?

Why is the internal energy classified Why is the internal energy classified as a state function, meanwhile work as a state function, meanwhile work and heat is not classified as a state and heat is not classified as a state function ?function ?

Can we warm up of a soap without Can we warm up of a soap without giving any additional amount of heat giving any additional amount of heat to the soup ? Explain itto the soup ? Explain it

A work can be done into a system at A work can be done into a system at a constant pressure, heat can also be a constant pressure, heat can also be tranferred to a system at a constant tranferred to a system at a constant volume. Is it possible to transfer volume. Is it possible to transfer heat to a system while maintaining heat to a system while maintaining the temperature of the system the temperature of the system constant ? Explain itconstant ? Explain it

A diatomic in a closed container has an A diatomic in a closed container has an initial temperature of 250oC, a pressure initial temperature of 250oC, a pressure of 105 N/m2, and a volume of 5 L. The of 105 N/m2, and a volume of 5 L. The gas undergoes an isobaric process to a gas undergoes an isobaric process to a pressure of 2 x 105 N/m2. a. Describes pressure of 2 x 105 N/m2. a. Describes the process above in a P-V diagramthe process above in a P-V diagram

b. Find the change in its internal energyb. Find the change in its internal energy

c. find the total work done by the gasc. find the total work done by the gas

Student ActivityStudent Activity Mention three general variables of Mention three general variables of

thermodynamicsthermodynamics What is state function ?What is state function ? Why is the internal energy classified as a state Why is the internal energy classified as a state

function, meanwhile work and heat is not function, meanwhile work and heat is not classified as a state function ?classified as a state function ?

Can we warm up of a soap without giving any Can we warm up of a soap without giving any additional amount of heat to the soup ? Explain itadditional amount of heat to the soup ? Explain it

A work can be done into a system at a constant A work can be done into a system at a constant pressure, heat can also be tranferred to a system pressure, heat can also be tranferred to a system at a constant volume. Is it possible to transfer at a constant volume. Is it possible to transfer heat to a system while maintaining the heat to a system while maintaining the temperature of the system constant ? Explain ittemperature of the system constant ? Explain it

Student Activity #2Student Activity #2

System absorbs 1500 J of energy from surrounding. At the same time 2200 J work done is given to the system. Determine the change of

internal energy of the system. Is temperature decreses or increases ?

Student Activity #3Student Activity #3

Two mol of ideal gas is expans from point I to point F with three difference way as shown in diagram below. Calculate the work done, change of internal energy, and calor in each way IAF, IF and IBF, state in joule

P(atm)

V(L)

4

1

2 4

A

I

FB

Student ActivityStudent Activity

Four mol of ideal gas in cylinder container change its conditional as shown in graphic P-V beside. Determine the work done, internal energy and calor if the gas is change from A to C thrue (a) ABC, (b) AC

500

200

0300 500 800

AB

C

V(cm3)

P(Pa)

Quiz (work in pairs)Quiz (work in pairs)

Three different processes act on system.

a. In process A, 42J of work are done on the system and 77J of heat are added to the system. Find the change in the system’s internal energy.

b. In process B. the system does 42 J of work and 77J of heat are added to the system. What is the change in the system’s internal energy ?

c. In process C, the system’s internal energy decreases by 120 J while the system performs 120 J of work on its surroundings. How much heat was added to the system ?

Student Activity #6Student Activity #6

An ideal gas is taken through the four processes shown in figure below. The changes in internal energy for three of these processes are as follows : UAB = + 82 J, UBC = +15 J, UDA = -56 J. Find the change in internal energy for the process from C to D

A

D C

B

volume

pre

ssu

re

Student Activity # 7Student Activity # 7a. Find the work done by a monoatomic ideal gas as it

expands from point A to point C along the path shown in figure below.

b. If the temperature of the gas is 220K at point A, what is its temperature at point C ?

c. How much heat has been added to or removed from the gas during this process ?

0 2 4 6 8 10

200

400

600

Pre

ssu

re

P(k

Pa)

Volume, V(m3)

A C

B

Student Activity #8Student Activity #8

During an adiabatic process, the temperature of 3.52 moles of monoatomic ideal gas drops from 485oC to 205oC. For this gas, find

a. The work it doesb. The heat it exchanges with its surroundings, andc. The changes in internal energy

Student Activity #9Student Activity #9

An ideal gas follows the three-part process shown in figure below. At the completion of one full cycle, find

a. The net work done by the systemb. The net change in internal energy of the systemc. The net heat absorbed by the system

0 1 2 3 4

100

50

150

Pre

ssu

re

P(k

Pa)

Volume, V(m3)

C

A

B

QuizQuiz

Suppose 57.5 moles of an ideal monoatomic gas undergoes the series of processes shown in figure below.

a. Calculate the temperature at the points A, B, and C.b. For each process, A-B, B-C, and C-A, state whether heat

enters or leaves the system, Explain in each case.c. Calculate the heat exchanged with the gas during each of

three process.

0 1 2 3 4

100

50

150

Pre

ssu

re

P(k

Pa)

Volume, V(m3)

C

A

B