Consider the following generic chemical equation whose AHrxn is unknown. Target: 2 A + 7 B 4X Instead, you are given two other equations for which the AHxn is known: 1) 4 C + 3 B → 2 X (AHXN = -1305 kJ) 2) C + X → A + B (AHxn = -205 kJ) %3D

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Chapter9: Energy And Chemistry
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Consider the following generic chemical equation whose AHXN is unknown.
Target: 2 A + 7 B
→ 4 X
Instead, you are given two other equations for which the AHrxn is known:
1) 4 C + 3 B
→ 2 X (AHrxn = -1305 kJ)
2) C + X
A + B (AHrxn = -205 kJ)
A) Add chemical equations 1 and 2 together using Hess's Law to obtain the target
equation. Clearly show which substances cancel and which don't.
B) Calculate AHxn for the target reaction. Show all work.
Parts C-E below are unrelated to A and B above, but are still part of Short Answer #3.
An ideal gas is contained in a 1.5 L moveable piston at STP.
Pext
C) Without performing any calculations, how would the volume change if the gas is NOT
ideal? Briefly explain (in about 1 sentence) how you know, based on the assumptions of
the Kinetic Molecular Theory (KMT).
D) If the ideal gas is expanded to 2.8 L by instantaneously decreasing pressure to 0.54
atm (at constant T), how much work (in Joules) was transferred by the gas? Assume that
the external pressure remains constant while the volume changes. Recall that 1 Latm =
101.3 J.
E) Assume that AE = 0 for the change in state described in part D. In this case, how much
heat was transferred by the expansion? Briefly explain in about 1 sentence why this
result makes physical sense using what you know about sign conventions.
Transcribed Image Text:Consider the following generic chemical equation whose AHXN is unknown. Target: 2 A + 7 B → 4 X Instead, you are given two other equations for which the AHrxn is known: 1) 4 C + 3 B → 2 X (AHrxn = -1305 kJ) 2) C + X A + B (AHrxn = -205 kJ) A) Add chemical equations 1 and 2 together using Hess's Law to obtain the target equation. Clearly show which substances cancel and which don't. B) Calculate AHxn for the target reaction. Show all work. Parts C-E below are unrelated to A and B above, but are still part of Short Answer #3. An ideal gas is contained in a 1.5 L moveable piston at STP. Pext C) Without performing any calculations, how would the volume change if the gas is NOT ideal? Briefly explain (in about 1 sentence) how you know, based on the assumptions of the Kinetic Molecular Theory (KMT). D) If the ideal gas is expanded to 2.8 L by instantaneously decreasing pressure to 0.54 atm (at constant T), how much work (in Joules) was transferred by the gas? Assume that the external pressure remains constant while the volume changes. Recall that 1 Latm = 101.3 J. E) Assume that AE = 0 for the change in state described in part D. In this case, how much heat was transferred by the expansion? Briefly explain in about 1 sentence why this result makes physical sense using what you know about sign conventions.
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