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Upper Secondary Chemistry · Interactive laboratory

Thermochemistry

Explore enthalpy, heat, activation energy and Hess’s law.
Developed by Dr. Georgios Malis
100% offline · HTML

Methane combustion

Exothermic reaction · Standard conditions
Interactive model
CH₄(g) + 2O₂(g) → CO₂(g) + 2H₂O(l)
Enthalpy / Reaction pathway
Uncatalyzed pathway Catalyzed pathway ΔH (level difference)
Reaction systemReleases heat
q of system < 0
To the surroundings
SurroundingsAbsorbs
q of surroundings > 0
−890 kJfor the equation as written
0,00 molξ = n₀ × fraction reacted
0,0 kJqₚ = ξ · ΔH
04 · Interactive exercise

Hess’s law in practice

We want to form CO(g) from C(s) and O₂(g). Choose which of the two equations to reverse.

(I) C(s) + O₂(g) → CO₂(g)

ΔH₁ = −394 kJ

(II) CO(g) + ½O₂(g) → CO₂(g)

ΔH₂ = −283 kJ

Select the correct transformations.
Target: C(s) + ½O₂(g) → CO(g). Identical species on both sides cancel algebraically.
05 · Mini experiment

Calorimetry

In an ideally insulated calorimeter, the aqueous surroundings change temperature. Calculate the heat transferred.

200 g
50 g500 g
+5 °C
−10 °C+12 °C
qof water = m · c · ΔT
200 × 4,18 × (+5) / 1000
+4,18 kJ
The water warms up: the system is exothermic.
Assume c = 4.18 J g⁻¹ °C⁻¹, negligible heat loss and negligible heat capacity of the vessel. Then qof the system = −qof water. Illustrative school-level calculation.
06 · Check your understanding

Thermochemistry mini quiz

Question 1 / 6