Playbook
Chemical Thermodynamics
121 q - 2.96/paper - 3% HARD. The first-law page is 50 questions of signs and 100 J per dm³ bar.
- Questions in the bank
- 121
- q/paper (2024–25 papers)
- 2.96
- Tagged HARD
- 3%
- Subtopics
- 6
Strand: Calculate
When you’ll see it
Heat and work for a system, ΔU against ΔH, a bond enthalpy or Hess's-law sum, or whether a reaction is spontaneous.
How this chapter is tested
121 q at 2.96 a paper, 3% HARD. The first-law page is 50 questions on its own: ΔU = q + w with the chemist's sign convention (work done ON the system is positive), w = −P_ext·ΔV, and 1 dm³ bar = 100 J.
ΔH = ΔU + Δn_g·RT (18 q) needs only the change in moles of GAS. Hess's law and bond enthalpies (21 q) add and subtract equations. Spontaneity (11 q) is the ΔG = ΔH − TΔS sign table: ΔH negative and ΔS positive is spontaneous at all temperatures.
The sub-skills
The distinct skills inside the chapter, in the order to learn them.
First law and signs
ΔU = q + w. Heat absorbed and work done on the system are positive. Expansion: w = −P_ext·ΔV.
Units
1 dm³ bar = 100 J; 1 L atm = 101.3 J.
ΔH and ΔU
ΔH = ΔU + Δn_g·RT, with Δn_g counted from gas moles only.
Spontaneity
ΔG = ΔH − TΔS; at equilibrium T = ΔH/ΔS; ΔG° = −2.303RT log K.
Traps to expect
Distractor shapes this chapter reuses. The Traps page covers the patterns that cut across chapters.
The physics sign convention
Chemistry counts work done ON the system as positive (ΔU = q + w). Physics' ΔU = q − w with work done BY the gas gives the same physics but a flipped w — mixing the two flips the answer.
Counting liquids in Δn_g
Only gas moles count. In H₂(g) + ½O₂(g) → H₂O(l), Δn_g = −1.5, not −0.5.
Learn it before you drill it
This chapter has full teaching notes — foundations, worked examples, self-checks and a per-subtopic mastery checkpoint. Read the notes once, then drill subtopic by subtopic below.
Chemical Thermodynamics notesDrill every chemical thermodynamics question
121 questions from the bank, scoped to 6 bundled subtopics.
Drill one subtopic at a time
The 6 subtopics this playbook covers, in catalog order.
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