Inv 8 Exp 2 - Heat of Formation & Hess Law

Elements in their standard state always have standard enthalpies of ________.

• -396 kJ/mol

• 33.2 kJ/mol

• 0.0 kJ/mol

• 396 kJ/mol

Tags

NGSS.HS-PS1-4

From the following data,

H₂ (g) + Cl₂ (g) →2HCl(g) ΔH°v = -185 kJ,

2H₂ (g) + O₂ (g) →2H₂O(g) ΔH° = -483.7 kJ,

calculate ΔH° for the following reaction.

4HCl(g) + O₂ (g) →2Cl₂ (g) + 2H₂O(g)

• 299 kJ

• -114 kJ

• -299 kJ

• 114 kJ

Tags

NGSS.HS-PS1-4

The enthalpies of combustion of C(s), H₂(g) and C₄H₉OH(l) (in kJ/mol) are as follows

C(s) + O₂(g) → CO₂(g) || ∆H=a

H₂(g) + ½O₂(g) → H₂O(l) || ∆H=b

C₄H₉OH(l) + 6O₂(g) → 4CO₂(g) + 5H₂O(l) || ∆H=c

What is the enthalpy change for the reaction shown below?

4C(g) + 5H₂(l) + ½O₂(g) → C₄H₉OH(l)

• c – 4a – 5b

• 2a + 10b - c

• 4a + 5b - c

• 2a + 5b + c

Tags

NGSS.HS-PS1-4

NGSS.HS-PS3-1

NGSS.HS-PS1-2

Calculate the enthalpy of reaction (ΔH).

4CO_{2 (g)} + 6H₂O _(g) → 2C₂H_{6 (g)} + 7O_{2 (g)}

ΔH_f^o [CO_2(g)] = -393.5 kJ

ΔH_f^o [H₂O_(g)] = -241.8 kJ

ΔH_f^o [C₂H_6(g)] = -84.7 kJ

• 550.6 kJ/mol

• 2855.4 kJ/mol

• -550.6 kJ/mol

• -3194.2 kJ/mol

Tags

NGSS.HS-PS1-4

NGSS.HS-PS3-1

What is the difference between calculating $\Delta H$   with bond energies versus with heats of formation?

• Bond energies are averages based on multiple scenarios of breaking bonds, heats of formation is the energy required to form a specific molecule from its elemental forms.

• Heats of formation are averages based on multiple scenarios of breaking bonds, bond energies is the energy required to form a specific molecule from its elemental forms.

• Bond energies are calculated using only lewis dot structures, but heats of formation requires a reference table

• Heats of formation helps calculate enthalpy, while bond energies helps calculate entropy

The standard state of elements when using heat of formations is (select all that apply):

• The state of the elements (solid, liquid, gas) at standard temperature and pressure.

• Diatomic gas molecules for H₂, N₂, O₂, F₂ and Cl₂

• Always a monoatomic gas with no net charge.

• A gas at its boiling point.

which of the following enthalpy changes represent the enthalpy change of formation?

• Mg(s) + Cl₂(g) → MgCl₂(s)

• Mg²⁺(g) + 2 Cl ^-(g) → MgCl₂(aq)

• O2(g) → 2 O(g)

• 2Mg (s) + O₂(g) → 2MgO(S)

The following is a thermochemical equation for the complete combustion of ethane:
2C₂H₆(g)+7O₂(g)→4CO₂(g)+6H₂O(g); ΔH=-3114 kJ/mol
If the activation energy of the reaction is 275 kJ per mol of ethane, the energy released, in kJ, during bond formation for the reaction as written above will be

• 2564
• 2839
• 3389
• 3664

Tags

NGSS.HS-PS1-4

NGSS.HS-PS3-1

What is still confusing? How can I help?