From bonding to thermodynamics
A second pathway moving from bonding and molecular shape to counting matter, reading chemical equations, reasoning about gases and understanding the first tools of thermodynamics.
By the end, you will be able to…
End-of-path challenge
Combine geometry, amount of substance and energy in one line of reasoning.
1. Why is CO₂ nonpolar overall despite polar C=O bonds?
Show the reasoned answer
Answer: Its linear geometry places two equivalent dipoles in opposite directions, so they cancel.
Explanation: Combine geometry, amount of substance and energy in one line of reasoning.
Method: Connect the definition to the mechanism described in the lesson: identify what changes and what remains fixed before drawing the conclusion.
2. For 2 H₂ + O₂ → 2 H₂O, 6 mol H₂ react with 2 mol O₂. Which reactant limits?
Show the reasoned answer
Answer: 2 mol O₂ require 4 mol H₂. O₂ is limiting; 2 mol H₂ remain and 4 mol H₂O can form.
Method: Start from the relation used, substitute each quantity with its unit, then check the order of magnitude and the final unit.
3. A change has ΔH = −40 kJ·mol⁻¹ and ΔS = −100 J·mol⁻¹·K⁻¹ at 298 K. Estimate ΔG.
Show the reasoned answer
Answer: Convert ΔS: −0.100 kJ·mol⁻¹·K⁻¹. ΔG = −40 − 298×(−0.100) ≈ −10.2 kJ·mol⁻¹, thermodynamically favorable under these conditions.
Method: Start from the relation used, substitute each quantity with its unit, then check the order of magnitude and the final unit.