Enthalpy of Formation

Enthalpy of Formation

By Angela Toh

Multiple Choice

ΔH value in an endothermic reaction is a positive number.

• True
• False

Multiple Choice

How can you convert Kelvin to Celcius?

• add 273
• subtract 273
• multiply by 273
• divide by 273

Multiple Choice

How much heat does an aluminum block absorb if 10.00 grams is heated from 25.0^oC to 50.0^oC? the specific heat of aluminum is 0.900J/g^oC

• 450

• -450

• 225

• -225

Multiple Choice

Which of the following equations represents the enthalpy change of combustion?

• 2C₄H₁₀(g) + 13O₂(g) → 8CO₂ (g) + 10H₂0(g)

• C₄H₁₀(g) +13/2O₂(g) → 4CO₂ (g) + 5H₂0(g)

• C₄H₁₀ + 9/2O₂ → 4CO (s)+ 5H₂O

• C₄H₁₀ + 5/2O₂ → 4C(s) + 5H₂O(g)

Multiple Choice

What is standard enthalpy of formation, ΔH_f^o?

• Heat change when 1 mole of gaseous ions is hydrated in water at 25^oC and 1 atm

• Heat change when 1 mole of compound is formed from its elements in their standard states at 25^oC and 1 atm

• Heat change when 1 mole of gaseous atom is formed from its elements at 25^oC and 1 atm

• Heat change when 1 mole of electrons is removed from 1 mole of gaseous atoms at ground state at 25^oC and 1 atm

Multiple Choice

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)

Multiple Choice

The amount of energy released or absorbed when one mole of a compound is formed from its elements

• heat of reaction
• heat of combustion
•  heat of completion
• heat of formation

Multiple Choice

How much heat is needed to form 40.0 dm³ of NO₂ from its elements at STP?

N₂+ 2O₂ -> 2NO₂ ΔH_rxn = +67.0kJ

• 134 kJ

• 33.5 kJ

• 59.0 kJ

• 38.0 kJ

Multiple Choice

Which of the following has a ΔH_f^o value of 0?

• Br₂(g)

• N(g)

• CO(g)

• Ne(g)

Fill in the Blanks

Use the H_f values provided below to calculate H_rxn for the reaction. (Exclude units in your answer)

CO_2(g) + N_2(g) ⟶ NO_(g) + CO_(g) ΔH = ?

Data:

CO(g) = -110 kJ/mol

CO2(g) = -394 kJ/mol

NO(g) = +90 kJ/mol

Multiple Choice

Calculate the enthalpy of the following reaction using the data provided below.

Ca(OH)₂ --> CaO + H₂O

ΔHf in kJ/mol:

Ca(OH)₂ -983.2

CaO -634.9

H₂O -285.5

• 62.8 kJ

• -62.8 kJ

• -1840.6

• 1840.6

Multiple Choice

Calculate enthalpy (in kJ) for these reactions and determine if reaction is exothermic or endothermic.

CaCO₃(s) --> CaO(s) + CO₂(g)

• 178.31, endothermic

• 178.31, exothermic

• -178.31, endothermic

• -178.31, exothermic

Multiple Choice

Calculate enthalpy (in kJ) for these reactions and determine if reaction is exothermic or endothermic.

CH₄(g) + Cl₂(g) --> CCl₄(l) + 2H₂(g)

• 60.60, endothermic

• 60.60, exothermic

• -60.60, endothermic

• -60.60, exothermic

Multiple Choice

Calculate enthalpy (in kJ) for these reactions and determine if reaction is exothermic or endothermic.

4NH₃(g) + 7O₂(g) --> 4NO₂(g) + 6H₂O(l)

• 1764.40, endothermic

• 1764.40, exothermic

• -1764.40, endothermic

• -1764.40, exothermic

Multiple Choice

Calculate enthalpy (in kJ) for these reactions and determine if reaction is exothermic or endothermic.

Ba(s) +2HCl(aq) --> BaCl₂(aq) + H₂(g)

• 524.20, endothermic

• 524.20, exothermic

• -524.20, endothermic

• -524.20, exothermic