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The First Law of Thermodynamics

Happy New Week.

The week's topics: UPDATED!!
First Law of Thermodynamics:
- the first law as it relates to the universe;
- revision of heat, work, the thermodynamic potentials (U, H, A, G); and
- the 1st Law and its application to Open Systems


"Thermodynamics is a branch of physics which deals with the energy and work of a system.
Thermodynamics deals only with the large scale response of a system which we can observe and measure in experiments. Small scale gas interactions are described by the kinetic theory of gases.
There are three principal laws of thermodynamics which lead to the definition of thermodynamic properties which help us to understand and predict the operation of a physical system." (NASA).

“The first law of thermodynamics is the application of the conservation of energy principle to heat and thermodynamic processes.” (All energy in the universe is accounted for). “The laws of thermodynamics are special laws upon which the other [natural] laws depend” (Physica…

Thermo Solved Questions

QUESTION 1- Constant Volume Heat Addition
(from www.msubbu.com)
A 28 liter rigid enclosure contains air at 140 kPa and 20oC. Heat is added to the container until the pressure reaches 345 kPa. Calculate the heat added.

SOLUTION:
Given: V = 28L= 0.028m (1L = 1dm3; 10dm = 1m so (10dm)3 = (1m)3)
P1 = 140 KPa
T1 = 20oC = 293K
P2 = 345KPa
∆Q = ?

From the 1st Law of Thermodynamics,
∆Q = ∆U + W

Introducing the reversible work terms,
∆Q = ∆U + P∆V

But at constant volume, P∆V = 0
So ∆Q = ∆U
And ∆Q = ∆U = mCp∆T

But what is m? Cp?

-m can be gotten from the formula PV = nRT, where n = m/M (mass/molecular mass)
m = nM, and n = PV/RT = (140 x 0.028)/(8.314 x 293)
n = 1.609 x 10^-3, and M air = 29, so m = 1.609 x 10^-3 x 29 = 0.0467kg

Good. Now,
-Cv is used, not Cp, because we are dealing wit constant volume here.
Cv air at 20C = 0.718KJ/KgC
Also, at constant V, P ∞ T

So P1/T1 = P2/T2 and T2 = 722K
and ∆Q = ∆U…

Undstanding Thermodynamics

Knowledge of today’s Thermodynamic principles came little by little to our ancestors . As time went on, they made educated guesses based on experiments; sometimes they were spot-on, other times they were wrong. According to MIT, “...Our predecessors faced problems and situations that they couldn't explain with existing principles in Physics and Mathematics. Consequently, they proceeded to create new theories and 'laws' verifying their hypotheses with experiments...”
The Historical Progression of Classical Thermodynamics:
The Preclassical Era (1600 - 1840)
People like Galileo, Black and Count Rumford developed Physics mainly, focusing on experiments. Towards the ending of this era, however, Joule and Carnot proposed the Work and Heat Concepts , leading to the next era---
The Classical Era (1840 – 1900)
Scientists like Maxwell, Clausius, Lord Kelvin and Boltzmann studied and further developed Physics, Mathematics and Mechanical Engineering, focusing on laws and postulates.
Gibbs…

1st Law of Thermo

SOME DEFINITIONS

SYSTEM: Region being considered, usually enclosed in a boundary

SURROUNDING: Region that is not under consideration

BOUNDARY: Demarcation between system and surrounding

MATTER: Anything at all, that has weight and occupies space

ENERGY: The ability to do work. Heat energy is usually implied in Chem. Eng

WORK: Product of the force applied and resulting distance moved

State of a System: The state of a system can be identified by property values (eg. pressure, temperature) required to reproduce the system.

Path of a System: Refers to the steps taken to reach certain property values

Simple Systems: Are devoid of any internal adiabatic, rigid, impermeable boundaries; no external force fields or internal forces. A simple system can be single or multi-phase.

Composite Systems: Are two or more simple systems

Open Systems: Allow matter, energy …

An Innovation 360 Experience-- 1st Hand Info

The Innovation 360° competition has come and gone, and speaking as one who had the privilege of participating in the competition, I say it was wonderful.
In case you were living under a rock during the entire duration of the British Council –sponsored competition, I have said a little bit about it in an earlier post—just click the link at the right or better yet, scroll down.
Okay, so I have neglected this blog for quite some time, so in the spirit of revival, I will quickly highlight a few things that I gained during the competition:

>>> Congratulations to the British Council on its 75th Anniversary—people celebrate birthdays all the time, with food, drink and general merry-making, but I see that it is even more admirable to give back to society while you are at it. The BC sponsored the six winners with UK Masters’ scholarships worth N3.5Million, as well as Virgin Atlantic plane tickets to and fro and monthly upkeep allowances… lucky fellas and chica menn! Well they all deserve…