Answer to Question #242190 in General Chemistry for KING

Question

Stearic acid (C18H36O2) is a typical fatty acid, a moleculewith a long hydrocarbon chain and an organic acid group (COOH) at the end. It is used to make cosmetics, ointments,soaps, and candles and is found in animal tissue as part of manysaturated fats. In fact, when you eat meat, chances are that youare ingesting some fats that contain stearic acid.

(a) Write a balanced equation for the complete combustion ofstearic acid to gaseous products.

(b) Calculate ∆H°rxnfor this combustion (∆H°f = -948 kJ/mol).

(c) Calculate the heat (q) in kJ and kcal when 1.00 g of stearicacid is burned completely.

(d) The nutritional information for a candy bar states that oneserving contains 11.0 g of fat

and 100 Calfrom fat (1 Cal =1 kcal). Is this information consistent with your answer in part (c)?

Answer 1

a)The balanced equation for the complete combustion of stearic acid to gaseous products is given below:

C18H36O2(s) +26 O2 (g) 18CO2(g) +18 H2O(l)

b) ∆H combustion = 18× ∆Hf of CO2 + 18×∆Hf of H2O - (1× Hf of (C18H36O2)+ 26(∆Hf of O2)

= 18(-394kj/mol) + 18(-242kJ/mol) -1(948 kJ/mol) + 26(0kJ/mol)

= -10500kJ/mol