Concept check: thermal chemical equation, Enthalpy change, Standard enthalpy cha

Question

Concept check: thermal chemical equation, Enthalpy change, Standard enthalpy change of reaction According to the following thermalchemical equation, CH3OCH3 (I) + 3 02 (g) 2 CO2 (g) + 3 H20 (l) --1450 u a. Is this reaction endothermic or exothermic? b. How many heat (kl) is involved to burn 1 mol of CH,OCH, ()? 1. c. How many heat (k)) is involved to burn 3 mol of CH,OCH3 ()? d. How many heat (k) is involved to burn 235 g of CH,0CHs ()? 2. When 24.3 g of Al is burned, 751 kJ heat is released. What is the enthalpy change (AH) of this reaction? anl (s) +302 (g) 2A403 (s)

Explanation / Answer

1)

a)

since delta H is negative, the reaction is exothermic

b)

from reaction, for 1 mol of CH3OCH3, heat involved = -1450 KJ

Answer: -1450 KJ

c)

from reaction, for 1 mol of CH3OCH3, heat involved = -1450 KJ

so, for 3 mol of CH3OCH3, heat involved = -3*1450 KJ = -4350 KJ

Answer: -4350 KJ

d)

Molar mass of CH3OCH3 = 2*MM(C) + 6*MM(H) + 1*MM(O)

= 2*12.01 + 6*1.008 + 1*16.0

= 46.068 g/mol

mass of CH3OCH3 = 235 g

we have below equation to be used:

number of mol of CH3OCH3,

n = mass of CH3OCH3/molar mass of CH3OCH3

=(235.0 g)/(46.068 g/mol)

= 5.101 mol

from reaction, for 1 mol of CH3OCH3, heat involved = -1450 KJ

so, for 5.101 mol of CH3OCH3, heat involved = -5.101*1450 KJ = -7396 KJ

Answer: -7396 KJ

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