Answer:
a. 181.5 kcal
Step-by-step explanation:
Step 1: Calculate the enthalpy of the process (ΔH°).
Let's consider the following process.
CO₂(s) → CO₂(g)
We can calculate the enthalpy of the process using the following expression.
ΔH° = ∑ np × ΔH°f(p) - ∑ nr × ΔH°f(r)
ΔH° = 1 mol × ΔH°f(CO₂(g)) - 1 mol × ΔH°f(CO₂(s))
ΔH° = 1 mol × (-393.5 kJ/mol) - 1 mol × (-427.4 kJ/mol) = 33.9 kJ
According to the balanced equation, 33.9 kJ are required to sublime 1 mole of CO₂.
Step 2: Convert 986 g of CO₂ to moles
The molar mass of CO₂ is 44.01 g/mol.
986 g × 1 mol/44.01 g = 22.4 mol
Step 3: Calculate the enthalpy needed to sublime 22.4 moles of CO₂
22.4 mol × 33.9 kJ/1 mol = 759 kJ
We can convert it to Kcal using the conversion factor 1 kcal = 4.184 kJ.
759 kJ × 1 kcal/4.184 kJ = 181.5 kcal