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NEET-UG and JEE Main Chemistry · Class 11

Hess's law of constant heat summation — NEET & JEE Questions

Hess's law of constant heat summation is a topic in Chemical Thermodynamics, a Class 11 Chemistry chapter of the NEET-UG and JEE Main syllabus. TestBudy holds 12 published NEET-UG and JEE Main questions on Hess's law of constant heat summation, each with the marking scheme of the real paper.

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Hess's law of constant heat summation MCQs with solutions

10 of the 12 published questions on this topic, exactly as they appear in a test. Answers and worked solutions come with your result rather than on this page.

  1. Question 1 · difficulty L1 · recall

    Hess's law states that the enthalpy change of a reaction depends on

    • A. initial and final states, not the path taken
    • B. the number of intermediate steps only
    • C. the reaction mechanism only
    • D. the catalyst used

  2. Question 2 · difficulty L2 · understanding

    If a thermochemical equation is reversed, its enthalpy change

    • A. changes sign
    • B. remains unchanged
    • C. becomes zero
    • D. is squared

  3. Question 3 · difficulty L2 · understanding

    If every coefficient in a thermochemical equation is multiplied by 2, the enthalpy change should be

    • A. multiplied by 2
    • B. divided by 2
    • C. unchanged
    • D. changed in sign only

  4. Question 4 · difficulty L2 · understanding

    Hess's law can be used because enthalpy is a

    • A. state function
    • B. path function
    • C. vector quantity
    • D. dimensionless constant

  5. Question 5 · difficulty L3 · application

    If A → B has ΔH=+20\Delta H=+20 kJ and B → C has ΔH=−50\Delta H=-50 kJ, what is ΔH\Delta H for A → C?

    • A. −30-30 kJ
    • B. +30+30 kJ
    • C. −70-70 kJ
    • D. +70+70 kJ

  6. Question 6 · difficulty L3 · application

    For A → B, ΔH=+40\Delta H=+40 kJ. What is ΔH\Delta H for B → A?

    • A. −40-40 kJ
    • B. +40+40 kJ
    • C. 0 kJ
    • D. +80+80 kJ

  7. Question 7 · difficulty L3 · application

    A reaction written for 1 mol product has ΔH=−100\Delta H=-100 kJ. What is ΔH\Delta H when the entire equation is multiplied by 3?

    • A. −300-300 kJ
    • B. −100-100 kJ
    • C. +300+300 kJ
    • D. −33.3-33.3 kJ

  8. Question 8 · difficulty L3 · application

    Given A → C, ΔH=−80\Delta H=-80 kJ and B → C, ΔH=−30\Delta H=-30 kJ, what is ΔH\Delta H for A → B?

    • A. −50-50 kJ
    • B. +50+50 kJ
    • C. −110-110 kJ
    • D. +110+110 kJ

  9. Question 9 · difficulty L4 · application

    Given C + O2 → CO2, ΔH=−394\Delta H=-394 kJ and CO + 1/2 O2 → CO2, ΔH=−283\Delta H=-283 kJ, what is ΔH\Delta H for C + 1/2 O2 → CO?

    • A. −111-111 kJ
    • B. +111+111 kJ
    • C. −677-677 kJ
    • D. +677+677 kJ

  10. Question 10 · difficulty L4 · application

    If X → Y has ΔH=+25\Delta H=+25 kJ and X → Z has ΔH=−10\Delta H=-10 kJ, what is ΔH\Delta H for Y → Z?

    • A. −35-35 kJ
    • B. +35+35 kJ
    • C. +15+15 kJ
    • D. −15-15 kJ

Common mistakes in Hess's law of constant heat summation

Recorded against questions in this topic that are not shown above, so none of these points at an answer you can see on this page.

  • Forgets to multiply the enthalpy of equation 2 by the same factor as its coefficients.
  • Reverses the chemical equation but not the corresponding enthalpy sign.

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