Introduction to Enthalpy

Enthalpy of Formation Notes and Questions

Proceed through the following, taking notes as you go. You will receive a grade based on your score on the questions.

Also, you can follow along in the textbook -- pages 186-190

Multiple Choice

What does the little zero ⁰ in ΔH_f⁰ mean?

• room temp of 25 degrees Celsius and 1 atm of pressure

• zero enthalpy and zero molarity

• no reaction

• freezing temp of zero degrees Celsius and zero atm of pressure

Multiple Choice

Enthalpy of formation is ______________.

• the enthalpy change in which one mole of a compound dissolves in water

• the enthalpy change in which one mole of a compound is decomposed into its elements

• the enthalpy change in which one mole of a compound is made from its elements

Multiple Select

Where can you find a table containing standard enthalpies of formation? (Select all that apply.)

• page 1,088 of the textbook

• in the senior parking lot

• posted on Canvas

• in the nucleus of the atom

Multiple Choice

According to Appendix C, in your book or on Canvas, the value of the enthalpy of formation, $$\Delta$$ $$H_f$$  , for FeO(s) is _____ kJ/mol.

• 60.75

• -705.6

• -271.9

• 0

Multiple Choice

According to Appendix C, in your book or on Canvas, the value of the enthalpy of formation, $$\Delta$$ $$H_f$$  , for  $$Cl_2$$  (g) is _____ kJ/mol.

• 60.75

• -705.6

• -271.9

• 0

Multiple Choice

According to Appendix C, in your book or on Canvas, the value of the enthalpy of formation, $$\Delta$$ $$H_f$$  , for  $$NO_2$$  (g) is _____ kJ/mol.

• 60.75

• 33.84

• -271.9

• 0

Multiple Select

Which of the following will have standard enthalpies of formation equal to zero? (Select all that apply.)

• H₂ (g)

• Hg (s)

• CO₂ (g)

• H₂O (l)

• Br₂ (l)

Multiple Choice

In a formation reaction, you must make ______ as the product.

• exactly 1 mole of a compound

• exactly 1 mole of an element

• multiple moles of a compound

• multiple moles of an element

Multiple Choice

Select the reaction that is a correct formation reaction for NaCl .

• Na (s) + Cl (s) --> NaCl (s)

• 2Na (s) + Cl₂ (g) --> 2 NaCl (s)

• Na (s) + 1/2 Cl₂ (g) --> NaCl (s)

• Na (g) + Cl₂ (g) --> NaCl (s)

Multiple Choice

Which of the following is the formation reaction for SO₃ (g)?

• S (s) + 3/2 O₂(g) --> SO₃ (g)

• SO₃ (g) --> S (s) + 3/2 O₂(g)

• S (s) + 3 O(g) --> SO₃ (g)

Multiple Choice

What is the formation equation for Pb(NO₃)₂ (s) ?

• Pb(NO₃)₂ (s)  $$\longrightarrow$$  Pb (s) + 2 NO₃^-(aq)

• Pb (s) + 2 NO₃^-(aq) $$\longrightarrow$$   Pb(NO₃)₂ (s)

• Pb(s) + N₂ (g) + 3 O₂ (g)  $\longrightarrow$   Pb(NO₃)₂ (s)

• Pb(NO₃)₂ (s)  $\longrightarrow$   Pb(s) + N₂ (g) + 3 O₂ (g)

Multiple Choice

Which of the following correctly shows how you would find ΔH for the reaction below?

C₃H₈ (g) + 5 O₂ (g) --> 3 CO₂ (g) + 4 H₂O (l)

• 3(-393.5) + 4(-285.83) - ((-103.85) +5(0)) kJ

• (-103.85) +5(0) - (3(-393.5) + 4(-285.83)) kJ

• (-285.83) +5(103.85) - (3(-393.5) + 4(-285.83)) kJ

• 3(-285.83) +4(103.85) - (5(-393.5) + 5(-285.83)) kJ

Here are a couple more practice problems for you to try setting up. The solution appears on the next slide.

Multiple Choice

Which of the following shows how you would calculate the ΔH for the following reaction?

Mg(OH)₂ (s) --> MgO (s) + H₂O (l)

• ^-924.7 - (-601.8 + ^-285.83) kJ

• ^-285.83 + 2 (452.4) - (3 (297.4) + ^-141) kJ

• -601.8 + ^-285.83 - (^-924.7) kJ

Multiple Choice

Which of the following shows how you would calculate ΔH for the following reaction?

N₂O₄ (g) + 4 H₂ (g) --> N₂ (g) + 4 H₂O (g)

• 1(0) + 4(9.66) - (9.66 + 4(-241.82)) kJ

• 1(0) + 4(-241.82) - (9.66 + 4(0)) kJ

• 1(0) + 4(463.3) - (0 + 285.3) kJ

Multiple Choice

Which of the following shows how your would calculate the ΔH for the reaction shown below?

SiCl₄(l) + 2 H₂O (l) --> SiO₂ (s) + 4 HCl (g)

• ^-910.9 + 4(^-92.3) - (^-640.1+ 2(^-285.83))

• ^-640.1+ 2(^-285.83) - (910.9 + 4(^-92.3))

• ^-145.5 + 4(^-35.5) - (^-336.9+ 2(^-850.7))