Thermodynamics

Chemistry · Class 11

Simulation · Chemistry · Class 11

Bomb or open cup: ΔU or ΔH?

"Bomb or open cup: ΔU or ΔH?" is a free, interactive Class 11 Chemistry simulation for NEET and JEE, built on the NCERT section "Calorimetry" in Thermodynamics. The same combustion is run in a sealed bomb (constant V, measures ΔU) and an open vessel (constant p, measures ΔH); the gap ΔngRT is drawn as a bar that changes when water is gas or liquid. NEET has asked about this idea 1 time in 10 years of papers. JEE Main asked 51 questions from this chapter across the 42 shifts Lumi has analysed (2017–2026).

From the lesson Calorimetry in Thermodynamics. Change the values and watch what happens.

Bomb or open cup: ΔU or ΔH?Chemistry · Class 11

What it shows

NCERT § "Measurement of ΔU and ΔH: Calorimetry"

The same combustion is run in a sealed bomb (constant V, measures ΔU) and an open vessel (constant p, measures ΔH); the gap ΔngRT is drawn as a bar that changes when water is gas or liquid.

Controls

3 to try

  • Segmentedfuel CH4 / C2H6 / C6H6 / glucose
  • Togglewater formed as liquid / gas
  • Slidertemperature 280–400 K

Try this

Choose the fuel and water state that make ΔH = ΔU exactly (Δng = 0, e.g. glucose with H2O(l)).

Common mistake

Counting liquid water in Δng.

In NEET

10 years of papers

Asked 1 time in 10 years of NEET.

See the past questions: Enthalpy and Hess's Law, Thermodynamics (chapter)

In JEE Main

42 shifts analysed

51 questions from Thermodynamics across the 42 JEE Main shifts Lumi has analysed (2017–2026).

The idea behind it

NCERT § "Measurement of ΔU and ΔH: Calorimetry"

  • Energy changes are measured by calorimetry: the reaction is run in a vessel immersed in a known amount of liquid, and the heat released or absorbed is found from the temperature change and the calorimeter's heat capacity.
  • A bomb calorimeter is a sealed steel vessel of constant volume, so no pressure-volume work is done and it measures ΔU.
  • In a bomb calorimeter the sample is burnt in pure oxygen, and the heat given out is found from the rise in temperature of the surrounding water.
  • Reactions carried out at constant (atmospheric) pressure in a simple calorimeter give q_p, which is ΔH.
  • To convert a bomb calorimeter ΔU into ΔH, use ΔH = ΔU + Δn_gRT with gaseous species only.

Questions

5 answers

What does the "Bomb or open cup: ΔU or ΔH?" simulation show?
The same combustion is run in a sealed bomb (constant V, measures ΔU) and an open vessel (constant p, measures ΔH); the gap ΔngRT is drawn as a bar that changes when water is gas or liquid.
What mistake does the "Bomb or open cup: ΔU or ΔH?" simulation fix?
A common mistake it clears up: counting liquid water in Δng.
Has NEET asked about this idea?
Yes. NEET has asked about this idea 1 time in 10 years of papers.
Does JEE Main ask questions from Thermodynamics?
Yes. JEE Main asked 51 questions from this chapter across the 42 shifts Lumi has analysed (2017–2026).
Is this simulation free?
Yes. It is free and runs in the browser on a phone or a laptop. It belongs to the lesson "Calorimetry" in Thermodynamics (Class 11 Chemistry).

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