CzHy + 502 3 CO2 + 4H20
5) How many moles of oxygen (O2) are needed to react to produce 4.8 moles of carbon dioxide
(CO2)

8 moles

Explanation:

C3H8(g) + 5O2(g) ---> 3CO2(g) + 4H2O(g)

The balanced equation above shows the combustion of propane, C3H8 (for x is 3; y is 8) in oxygen, O2 to yield carbon dioxide, CO2 and water, H2O

The mole ratio on combustion are as follows:

5 moles of O2 react to produce 3 moles of CO2

Z mole of O2 react to produce 4.8 moles of CO2

To get the value of Z, cross multiply

4.8 moles x 5 mole = 3 mole x Z

24 = 3Z

Divide both sides by 3

24/3 = 3Z/3

8 = Z

Thus, in the combustion of propane, 8 moles of oxygen (O2) are needed to react to produce 4.8 moles of carbon dioxide (CO2)

your answer is a. the enthalpy of formation for a pure element in its standard state is always positive.