Determine the enthalpy change when 19.4 g of carbon is reacted with oxygen according to the reaction
A) 636 kJ
C) -636 kJ
D) -7.64 kJ
E) 6.76 kJ

Question

Determine the enthalpy change when 19.4 g of carbon is reacted with oxygen according to the reaction 
A) 636 kJ 
C) -636 kJ 
D) -7.64 kJ 
E) 6.76 kJ

Quizplus · Accepted Answer

The given reaction is: C(s) + O2(g) -> CO2(g)

From the balanced equation, we can see that 1 mole of carbon reacts with 1 mole of O2 to produce 1 mole of CO2.

The molar mass of carbon is 12.01 g/mol.

Therefore, the number of moles of carbon in 19.4 g of carbon = (19.4 g) / (12.01 g/mol) = 1.615 mol

According to the balanced equation, 1.615 mol of carbon reacts with 1.615 mol of O2 to produce 1.615 mol of CO2.

The enthalpy change for the reaction of 1 mole of carbon with oxygen to produce carbon dioxide is -393.5 kJ/mol (given in standard tables).

Therefore, the enthalpy change for the reaction of 1.615 mol of carbon with oxygen to produce carbon dioxide is:

= (-393.5 kJ/mol) x 1.615 mol
= -635.59 kJ/mol

Rounding off to three significant figures, we get -636 kJ, which is the answer choice C.

Determine the Enthalpy Change When 19