TestUstad

Free Hess's Law MCQs with Answers

11 Hess's Law MCQs from Chemistry, each with the correct answer and a written explanation of why it is correct. Free and unlimited, with no account needed.

Hess's law states that the enthalpy change of a reaction is independent of the route because enthalpy is a state function. Calculations involve reversing and adding thermochemical equations, using standard enthalpies of formation or combustion, and finding an unknown reaction enthalpy without confusing enthalpy change with reaction rate.

Last updated

11 questions

1. Hess's law states that the enthalpy change of a reaction

Fairly easy
  • A. depends on the number of steps taken
  • B. is the same whether the reaction occurs in one step or several
  • C. is always negative
  • D. depends on the catalyst used

Explanation: Because enthalpy is a state function, the total change depends only on the initial and final states, so a reaction that cannot be measured…

Read the full explanation →
Correct answer: is the same whether the reaction occurs in one step or several

2. Given that C + O2 gives CO2 has an enthalpy change of minus 393 kJ per mole, and CO + half O2 gives CO2 has an enthalpy change of minus 283 kJ per mole, the enthalpy of formation of carbon monoxide is

  • A. minus 676 kJ per mole
  • B. plus 110 kJ per mole
  • C. minus 110 kJ per mole
  • D. minus 283 kJ per mole

Explanation: Forming carbon monoxide and then burning it must total the same as burning carbon directly, so the unknown equals minus 393 minus the…

Read the full explanation →
Correct answer: minus 110 kJ per mole

3. Enthalpy change can be_________________?

  • A. calculated by Hess law
  • B. can be measured by calorimeter
  • C. both A and B
  • D. none

Explanation: An enthalpy change can be obtained experimentally from heat measurements in a calorimeter or calculated indirectly using Hess's law by…

Read the full explanation →
Correct answer: both A and B

4. The ΔHof for CO2(g), CO(g) and H2O(g) are −393.5, −110.5 and −241.8 kJ mol−1 respectively. The standard enthalpy change (in kJ) for the reaction: CO2(g) + H2(g) → CO(g) + H2O(g) is :

  • A. 524.1
  • B. 41.2
  • C. −262.5
  • D. −41.2

Explanation: The standard enthalpy change for a reaction can be calculated using the formula: ΔHreaction = ΣΔHf (products) - ΣΔHf (reactants).

Read the full explanation →
Correct answer: 41.2

5. The net heat change in a chemical reaction is the same whether it is brought about in two or more different ways in one or several steps. This is known as:

  • A. Henry's law
  • B. Hess's law
  • C. Joule's principle
  • D. Dalton's law

Explanation: Hess's Law is a fundamental principle in thermochemistry, asserting that the total enthalpy change during a chemical reaction is the same…

Read the full explanation →
Correct answer: Hess's law

6. Standard enthalpy of combustion of graphite at 25 °C is -393.51 kJ mol-1 and that of diamond is -395.41 kJ mol-1. The enthalpy change for graphite is:

  • A. -1.91
  • B. +2.1
  • C. -2.1
  • D. +1.91

Explanation: -2.1: This option suggests a negative value for the enthalpy change of graphite, and it is the correct answer.

Read the full explanation →
Correct answer: -1.91

7. Combustion of graphite to form CO2 can be done by two ways. Reactions are given as follows: 1.C + O2 -> CO2 ∆H = -393.7 kJ mol-12.C + ½O2 -> CO ∆H = ?3.CO + ½O2 -> CO2 ∆H = -283 kJ mol-1What will be the enthalpy of the formation of CO?

  • A. -676 kJ mol-1
  • B. -110 kJ mol-1
  • C. 110 kJ mol-1
  • D. 676 kJ mol-1

Explanation: Writing equation 1 as it is and flipping equation 3: 1.C+02--> CO2 H=-393.7 kJ 3.CO2 --> CO +1/2O2 H=+283 kJ Adding these two equations…

Read the full explanation →
Correct answer: -110 kJ mol-1

8. Hess's law is analogous to:

  • A. Law of heat summation
  • B. 1st law of thermodynamics
  • C. Law of increasing entropy
  • D. Law of heat exchange

Explanation: Hess's Law is a direct consequence of the First Law of Thermodynamics and the fact that enthalpy is a state function.

Read the full explanation →
Correct answer: 1st law of thermodynamics

9. The standard enthalpy changes of formation of iron (II) oxide, FeO(s), and aluminum oxide, Al2O3(s) are -266 kJ mol-1 and -1676 kJ mol-1 respectively. What is the enthalpy change under standard conditions for the following reaction? 3FeO(s) + 2Al(s) → 3Fe(s) + Al2O3(s)

  • A. +878 kJ mol-1
  • B. -1942 kJ mol-1
  • C. -878 kJ mol-1
  • D. -2474 kJ mol-1

Explanation: The explanation for this question will be added soon.

Read the full explanation →
Correct answer: -878 kJ mol-1

10. The net enthalpy change in a chemical reaction is same whether it is brought about in two or more different ways in one or several steps. It is known as:

  • A. Joule's law
  • B. Law of conservation of energy
  • C. Hess's law
  • D. Henry's law

Explanation: According to Hess's law, the thermal effects of a reaction depends upon the initial and final conditions of the reacting substances.

Read the full explanation →
Correct answer: Hess's law

11. The net heat change in a chemical reaction is smae weather it takes place in one ste or several steps. This law is known as:

  • A. First law of thermodynamics
  • B. Henery's law
  • C. Hess's law
  • D. Joule's law

Explanation: Option A: The first law of thermodynamics states that energy can neither be created nor destroyed, only altered in form. Hence incorrect.

Read the full explanation →
Correct answer: Hess's law
Start Free Hess's Law Practice MCQs Test

Hess's Law MCQs: common questions

Are these Hess's Law MCQs free?

Yes. All Hess's Law MCQs from Chemistry are free on TestUstad, with unlimited attempts and no account needed. Nothing on this page is a sample or a trial.

How many Hess's Law MCQs are on this page?

There are 11 Hess's Law MCQs in the Chemistry bank, shown 20 to a page with the correct answer and an explanation on each.

Does every Hess's Law MCQ have an explanation?

Yes. Each Hess's Law question shows the correct option and a written explanation of why it is correct, so a wrong answer teaches you something rather than just being marked wrong.

Can I take a timed Hess's Law test?

Yes. The practice button on this page starts a free Hess's Law test drawn from the Chemistry bank. It marks each answer instantly, gives you a score at the end, and can be retaken as many times as you like.