A system, containing ideal gas only, is compressed at constant temperature by an
ID: 1001472 • Letter: A
Question
A system, containing ideal gas only, is compressed at constant temperature by an opposing pressure greater than the internal pressure. Which of the following statements is true? Heat must flow into the system. No work is done by or on the system if the opposing pressure is constant. Work is done by the system. Considering only PV work, the energy of the system is lowered. None of the above. Which of the following reactions would you expect to have the highest delta S degree? H_2(g) + F_2(g) rightarrow 2 HF(g) O N_2(g) + 0_2(g) - 2 NO(g) O 3 H_2(g) + N_2(g) rightarrow 2 NH_3(gr) O 2 NH_3(g) + 2 0_2(g) - N_20(g) + 3 H_2(g) O 2 F_2(g) + 2 H20(g) - 02(g) + 4 HF(g)Explanation / Answer
1) In an Isothermal compression work is done on the system by the surrounding.
Hence we rulled out option-3)
In a compression heat will flow out of the system as kinetic energy decreases (Hence we rulled out option- 1) and energy of system lowers down.
Hence Answer is option-4.
Considering only PV work, the energy of the system is lowered.
Q = = nRT ln(V2/V1)
Q = nRT ln(P1/P2)
As compression occurs we expect P1 < P2 hence ln(P1/P2) = –ve and,
Q = –ve
Heat energy decreases.
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9) Entropy is the measure of the disorderness in the system. As disorder increases entropy also increases.
Also gaseous state is the most disorderd state of all states.
Hence the reaction accompanied with formation of gaseous product or more number of gaseous product are with greater entropy change Sorxn.
On observation of given reaction it’s clear that the last reaction,
2F2 (g) + 2H2O (g) ----------> O2 (g) + 4HF (g)
Have,
Numeber of gaseous reactant = 2 + 2 = 4
Number of gaseous products = 1 + 4 = 5
I.e. reaction accompanied with formation of more number of gaseous product that reactants and hence for this reaction we expect highest Sorxn. Value.
Answer option-5
For the reaction in option-3 i.e. 3H2(g) + 2N2(g) -----> 2NH3 (g) there is decrease in number of gaseous species and hence entropy will lower for this reaction.
In rest options number of gaseous reactants = Number of gaseous products.
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