Consider the following reaction. 2 Mg(s) + O2(g) 2 MgO(s) ΔH = -1204 kJ?

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2016-05-30 11:51 pm

(b) Calculate the amount of heat transferred when 2.4 g of Mg(s) reacts at constant pressure.

(c) How many grams of MgO are produced during an enthalpy change of 96.0 kJ?

(d) How many kilojoules of heat are absorbed when 7.90 g of MgO(s) are decomposed into Mg(s) and O2(g) at constant pressure?

更新1:

2 Mg(s) + O2(g) 2 MgO(s) ΔH = -1204 kJ

回答 (1)

fooks

2016-05-31 12:02 am

(b)
2Mg(s) + O₂(g) → 2MgO(s) ...... ΔH = -1204 kJ

Molar mass of Mg = 24 g/mol
No. of moles of Mg reacted = (2.4 g) / (24 g/mol) = 0.1 mol

According to the thermochemical equation, 1204 kJ of heat is transferred when 2 moles of Mg reacts.
Amount of heat transferred = (1204 kJ) × (0.1/2) = 60.2 kJ

(c)
According to the thermochemical equation, 1204 kJ of heat is transferred when 2 moles of MgO is formed.
Number of moles of MgO formed = (2 mol) × (96.0/1204) = 0.159 mol

Molar mass of MgO = (24 + 16) g/mol = 40 g/mol
Mass of MgO produced = (40 g/mol) × (0.159 mol) = 6.36 g

(d)
Molar mass of MgO = 40 g/mol
No. of moles of MgO produced = (7.90 g) / (40 g/mol) = 0.198 mol

According to the thermochemical equation, 1204 kJ of heat is transferred when 2 moles of MgO is formed.
Amount of heat absorbed = (1204 kJ) × (0.198/2) = 119 kJ

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