Question

6-5. During the combustion of 10.0 g of octane, CH18, 479.0 kcal is released? Write a balanced equation for the combustion reaction What is the sign of AH for this reaction? How much energy is released by the combustion of 1.00 mol of C8H18 How many grams and how many moles of octane must be burned to release 450.0 kcal? How many kilocalories are released by the combustion of 17.0 g of C.Htc? 6-6 If I burn 0.315 moles of hexane (C6H14) in a bomb calorimeter containing 5.65 liters of water, what's the molar heat of combustion of Hexane if the water temperature rises 55.4 C? The density of water is 1 gram/mL. The heat capacity of water is 4.184 J/g C. (Note, we are not burning 1 mole of hexane, we are burning less than 1 mole.) 6-7 Calculate the specific heat of gold if it required 48.0 joules of heat to warm 25.0 grams of gold from 40.0 C to 55.0 C.

Answer 1

2 C₈H₁₈ + 25 O₂ = 18 H₂O + 16 CO₂

it is exothermic so sign is negative.

Moles in 10g = 10/molecular weight

= 10/114

= 0.087 moles

So 0.087 mole releases 479 kcal

1 mole will release= 479/0.087

= 5505.74 kcal

479 kcal is released from 10 g

1 kcal will be released from 10/479

450 k cal = (10/479)X 450

= 9.39 g

Moles = 9.39/114

= 0.082

10 g gives 479 kcal

1 g = 479/10

17 g = (479/10) X 17

= 814.3 kcal.