Question

When 1 mol of methane is burned at constant pressure, −890 kJ/mol of energy is released as heat. If a 3.72 g sample of methane is burned at constant pressure, what will be the value of ∆H? (Hint: Convert the grams of methane to moles. Also make sure your answer has the correct sign for an exothermic process.) Answer in units of kJ.

Answer 1

-206.9kJ

Step-by-step explanation:

Heat of combustion = -890kJ/mol

Mass of methane burnt = 3.72g

Unknown:

Heat liberated = ?

Solution:

Heat of combustion is the heat liberated when one mole of an element or compound is burnt completely in excess oxygen gas.

To solve this problem;

Find the number of moles of methane;

Number of moles =
`(mass)/(molar mass)`

Molar mass of CH₄ = 12 + 4(1) = 16g/mol

Number of moles =
`(3.72)/(16)` = 0.23moles

Now, heat liberated by 0.23mol of methane = -890kJ/mol x 0.23mol

= -206.9kJ