1. Gasoline is comprised of many different compounds, but one of them is octane,

Question

1. Gasoline is comprised of many different compounds, but one of them is octane, CaH The combustion of liquid octane with oxygen gas yields two products, carbon dioxide and water vapor a. Write a balanced chemical equation showing this combustion reaction. Which element is being oxidized, and which reduced, in this reaction? (if this isn't immediately clear, think it through, starting with what you do know for certain) b. Assume that the enthalpy of formation of liquid octane is -250.0 kJ/mole. What is the enthalpy of combustion for octane (how much heat is released when one mole of octane is burned?)? Be sure to show your work. c. A layer of copper welded to the bottom of a skillet weighs 125 g. How much heat is needed to raise the temperature of the copper layer from 25 °C to 300°C?. The specific heat capacity of copper is 0.387 (J/g-K). 2.

Explanation / Answer

Ans 1 :

a) The combustion reaction for the octane is given as :

2C8H18 (l) + 25O2 (g) = 16CO2 (g) + 18H2O (g)

b) when the element gets an increase in its oxidations state , it is said to be oxidised , and when its oxidation state decreses , it is reduced.

So here :

Hydrogen is oxidised

Oxygen has been reduced

c) The enthalpy of combustion of octane can be calculated by subtracting the formation enthalpy of octane from that of products.

The formation enthalpy of CO2 and H2O is -394 kJ and -286 KJ respectively.

So here :

= 16(-394) + 18(-286) - 2(-250)

= -10952 KJ for two moles

So for one moles : -10952 / 2

= -5476 KJ/mol

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