Chemical Reactions (1 Viewer)

[Forbidden.]

Q:


Petrol burns oxygen in a complete reaction to form carbon dioxide and water.
How many grams of oxygen are needed to fully burn 500g petrol ?
Also, calculate the mass of the products formed.

A:

Spoiler

Step 1: Balance the equation


2C₈H₁₈ + 25O₂ = 16CO₂ + 18H₂O


Step 2: Solve


2C₈H₁₈ =

(228g/228) x 500g = 500g


25O₂ =

(800g/228) x 500g = 1754g


16CO₂ =

(704g/228) x 500g = 1544g


18H₂O =

(324g/228) x 500g = 711g


Step 3: Finalise your answer

500g Petrol fully burns 1754g of Oxygen in a complete combustion to form 1544g of Carbon Dioxide gas and 711g of Water

Could anyone provide suggestions or a more simple way of solving equations by reducing the amount of steps or implementing shortcuts ?

 

[Riviet]

Spoiler

2C₈H₁₈ =

(228g/228) x 500g = 500g

The only thing that I can see that would shorten your working by about 10-15 seconds is neglecting this line; the mass of the fuel is given in the question so there isn't a need to show that working.

The only other thing might be your chemical equation; divide it all by two and you get 1 mole of fuel which might make it easier when working out the masses of the the other reactants/products.

 

[Forbidden.]

The only thing that I can see that would shorten your working by about 10-15 seconds is neglecting this line; the mass of the fuel is given in the question so there isn't a need to show that working.

The only other thing might be your chemical equation; divide it all by two and you get 1 mole of fuel which might make it easier when working out the masses of the the other reactants/products.

Uhh it would turn out as ..

C₈H₁₈ + 12.5O₂ = 8CO₂ + 9H₂O

You see, when working with moles, I strongly prefer integers as it makes calculations much more easier ...

Thanks for the

the mass of the fuel is given in the question so there isn't a need to show that working."

 

[Riviet]

Are we meant to know the formula for petrol ????

Well there isn't a specific formula for petrol, octane is just the main component of petrol. We are required to know the formula of simple alkane molecules like methane, butane, etc.