a) what does the first law of thermodynamics state? (ii) All process must 12 mar

Question

a) what does the first law of thermodynamics state? (ii) All process must 12 marks] thermodynamics abide by the first law of however the first law of allows for some non-natural processes. Give an example. 12 marks] (iii) How does the second law of thermodynamics correct the above problem with the first law? [1 marks b) Consider the change in entropy of 2.00 kg of granite when it is heated from -20°C to 20 by placing it in contact with a heat reservoir at 80°C. Note: c 790 J/kg K granite (i) Make an estimate of the entropy change (using a average 12 mark (ii) Calculate the exact entropy change. temp) 2 mark (iii) What is the percentage difference between (i and (ii)? [1 mari (iv) Does the entropy of the surroundings change? If yes, by how much? 12 mar (v) What is the total entropy change of the entire system? [1 mar c) (i) What are thermodynamic potentials? [2 ma

Explanation / Answer

1)

The 1st Law of Thermodyamics simply states that energy can be neither created nor destroyed (conservation of energy). (or) When a definite amount of work is done, a certain amount of heat is produced and vice-versa.

dQ =dU+dW

b)

Some aspects of the First Law of Thermodynamics can seem confusing. A burning log in the fireplace seems to violate the principles of conservation of matter/energy. Burning the log appears to create energy and destroy matter. In reality, the energy and matter are only changing place and form, they are not being created or destroyed. The wood in the log has chemical potential energy, which is released when it is burned. This released energy appears in the form of heat and light. The matter of the log is changed into smoke particles, ash, and soot. The log’s total energy and mass before burning are the same as the mass and energy of the soot, ash, smoke, heat and light afterwards.

The First Law of Thermodynamics applies to all matter and energy, no matter how much or what the conditions are. Looking at bigger and bigger systems of matter and energy eventually leads to a question: where did all of the matter and energy in the universe come from? The Second Law of Thermodynamics shows us that all of the energy in the universe is moving towards a less “useable” form. However, the First Law of Thermodynamics shows us that nothing in the physical universe can create or destroy that matter or energy. If nothing natural can create matter or energy, then something

supernatural must have created them.

c)

The first law of thermodynamics gives equivalnece between the quantity of heat and mechanical work or vice-versa. Thus, heat and mechanical work both ate interconvertible.The first law does not throw any light on the limitation and condition for this conversion. i.e., how much heat is converted into work and whether the transformation itself can take or not. The answer of the above question is the second law of thermodynamics.

c)

Four quantities called "thermodynamic potentials" are useful in the chemical thermodynamics of reactions and non-cyclic processes. They are internal energy(U), the enthalpy(H), the Helmholtz free energy(F) and the Gibbs free energy(G).

The four thermodynamic potentials are related by offsets of the "energy from the environment" term TS and the "expansion work" term PV. A mnemonic diagram suggested by Schroeder can help you keep track of the relationships between the four thermodynamic potentials.

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