Worksheet: Molar Energy Units

In this worksheet, we will practice using Avogadro's number to convert between molar energies and the energies of single bonds.

Q1:

The molar bond energy of F2 is 159 kJ/mol. Calculate the energy of one FF bond.

  • A1.65×10 J
  • B2.64×10 J
  • C9.58×10 J
  • D3.79×10 J
  • E2.55×10 J

Q2:

What is Avogadro’s number to 3 significant figures?

  • A6.02×10
  • B6.71×10
  • C10.0
  • D3.14
  • E1.38×10

Q3:

3.70 mol of ClCl bonds release 888 kJ of energy when they form. How much energy is released when 1,000ClCl bonds form?

  • A3.99×10 J
  • B1.48×10 J
  • C3.99×10 J
  • D1.48×10 J
  • E4.01×10 J

Q4:

Which of the following quantities of bonds requires the most energy to break?

  • A5.8molII(148kJ/mol)
  • B1.0molCC(835kJ/mol)
  • C2.0molHCl(428kJ/mol)
  • D2.0molHH(436kJ/mol)
  • E1.7molOO(494kJ/mol)

Q5:

Every molecule of iodine, I2, has an iodine–iodine bond, II. The energy required to break one of these bonds is 2.51×10 J. How much energy is required to break 1.00 mole of these II bonds?

  • A4.17×10 J
  • B3.44×10 J
  • C1.51×10 J
  • D2.51×10 J
  • E9.01×10 J

Q6:

The energy of the hydrogen–hydrogen bond in H2 is 436 kJ/mol. Which of the following is an equivalent description of the bond energy in hydrogen?

  • A436 kJ of energy is required to form the hydrogen–hydrogen bonds of 6.02×10 hydrogen molecules.
  • BFor every hydrogen–hydrogen bond in a hydrogen molecule formed, 436 kJ of energy is released.
  • C436 kJ of energy is released when the hydrogen–hydrogen bonds of 6.02×10 hydrogen molecules are broken.
  • DFor every hydrogen–hydrogen bond in a hydrogen molecule broken, 436 kJ of energy is released.
  • E436 kJ of energy is required to break the hydrogen–hydrogen bonds of 6.02×10 hydrogen molecules.

Q7:

What is the SI unit for energy?

  • AJoule (J)
  • BMole (mol)
  • CWatt (W)
  • DKilogram (kg)
  • EElectron volt (eV)

Q8:

The specific heat capacity of a substance is usually given in units of joules per gram per degree Celsius. From these units, which of the following statements best describes specific heat capacity?

  • AThe amount of energy needed to raise the temperature of 1 gram of a substance by 1C
  • BThe temperature of a substance that is equal to the amount of energy multiplied by its mass
  • CThe amount of substance that can be produced when one joule of energy is raised by 1C
  • DThe amount of energy formed when 1 gram of a substance reaches a specific temperature
  • EThe mass of a substance needed to raise the temperature by 1C

Q9:

A single HBr bond has an energy of 6.14×10J. What is the molar bond energy for HBr? Give your answer to the nearest whole number.

Q10:

It takes approximately 2.757×10 J of energy to break all the bonds in a single molecule of methane, CH4. What is the average molar bond energy for CH bonds? Give your answer to the nearest whole number.

Q11:

4.6 g of a fuel is found to produce 3,965 J of heat energy. If the 𝑀 of the fuel is 46 g/mol, what is the molar enthalpy change?

  • A39.65 kJ/mol
  • B18.24 kJ/mol
  • C2.52 kJ/mol
  • D78.36 kJ/mol
  • E86.20 kJ/mol

Q12:

Which of the following are units for the molar enthalpy change of a reaction, Δ𝐻?

  • Amol/dm3
  • BC/atom
  • CkJ/mol
  • Dcm3/s
  • Eg/mol

Q13:

It is estimated that the average adult should consume around 2,000 kcal per day to maintain a healthy lifestyle. What is this value in units of kilojoules?

Q14:

A food manufacturer determines that the energy content of one slice of their new bread is 400 kJ. What value is this in kilocalories? Give your answer to 1 decimal place.

Q15:

A chocolate bar is found to contain 228 kcal. What value is this in units of kilojoules? Give your answer to the nearest whole number.

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