The combustion of propane may be described by the chemical equation C3H8(g)+5O2(g)⟶3CO2(g)+4H2O(g) How many grams of O2(g) are needed to completely burn 73.7 g C3H8(g)? mass O2: g O2

Question

It is for the Chemistry Homework

Answer 1

I've seen other questions like this on the platform answered, so I'll try to break each step down a little further.

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First, find the molecular weight of C₃H₈ from the periodic table:

MW Carbon (C) = 12.01g/mol

MW Hydrogen (H) = 1.01 g/mol

3 C = 12.01 g/mol x 3 moles = 36.03 grams

8 H = 1.01 g/mol x 8 moles = 8.08 grams

Add the masses of the carbon and hydrogen together

36.03 grams C

+ 8.08 grams H

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44.11 grams/mole is the molecular weight of C₃H₈

So the number of moles in 73.7 grams of C₃H₈ is calculated like so:

73.3 grams C₃H₈ × 1 mole C₃H₈ = 1.66 moles C₃H₈

44.11 grams

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In order to know how much oxygen it takes to completely react with/burn up 1.66 moles C₃H₈, we need to convert the moles of C₃H₈ to moles of O₂.The only way we can do this is through the balanced equation since it's the only way to relate the two molecules.

From the balanced equation in the problem, we see on the left side that there are 5 O₂ for every 1 C₃H₈. You could say they are in a 5:1 ratio. (5 mole O₂ : 1 mole C₃H₈)

We have 1.66 moles C₃H₈ so:

1.66 moles C₃H₈ x 5 moles O₂ = 8.3 moles O₂

1 mole C₃H₈

This means that it takes 8.3 moles of O₂ to completely burn up the 1.66 moles of C₃H_8.

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Now we can look at what the question is actually asking us: How many grams of O₂ does it take to burn up the C₃H₈?

Now we can use the molecular weight of O₂ to convert moles of O₂ to grams of O₂. This is somewhat the reverse of what we did in the first part of the problem with C₃H₈.

First, we calculate the molecular weight of O₂.

MW Oxygen (O) = 15.9999 g/mole

2 O = 15.9999 g/mol x 2 moles = 31.9998 grams

We only have one element, so the molecular weight of O₂ is 31.99 grams/mole

So we use this to convert the moles of oxygen to the grams of oxygen that the problem requires.

8.3 moles O₂ x 31.99 grams = 265.52 grams O₂

1 mole O₂

So it takes 265.52 grams of O₂ to completely burn up 73.7 grams (aka 1.66 moles) of C₃H₈!

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Hope this helps!

Answer 2

So for this question, you only need to focus on the reactants side of the equation (since the question is only asking you about the reactants and nothing about the products).

According to your provided equation, it takes 5 moles of oxygen (O₂) to initiate a complete reaction with one mole of propane (C₃H₈).

The easiest way to set up problems such as these is to find out what substance you are starting with, and what you are trying to solve for so we can use the appropriate conversion factors. So we are starting with the mass of propane (73.7 grams), and we want to convert this quantity into grams of oxygen using stoichiometric coefficients. To solve this, we will need the stoichiometric coefficients for oxygen and propane (so we can relate moles of propane to moles of oxygen). These two react in a (5:1 ratio). We also need the molar masses of oxygen and propane so we can convert from mass units to molar quantities and vice versa. The molar mass of propane is 44.1 grams/mole, the molar mass of O₂ is 31.98 grams / mole.

Your conversion should look something like this:

73.7 grams C₃H₈ (1 mole C₃H₈ / 44.1 grams) (5 moles O₂ / 1 mole C₃H₈) (31.98 grams O₂ / 1 mole O₂)

= 267.23 grams of O₂ are required to react with 73.7 grams of propane.

If you are struggling with writing conversion factors use the general formula:

Given Units (Desired Unit / Given Unit) = Desired Unit.

By dividing a value with a given unit by another value with the same unit, those units will cancel. Multiplying this number by a value with the units you are trying to convert to will give you your desired units.

For example: The molar mass of propane is 44.1 grams/mole (1 mole of propane has a mass of 44.1 grams).

By dividing the given mass of propane by the mass of one mole of propane, your mass value gets converted into a molar quantity. This molar quantity can then be used to relate the moles of propane to the moles of oxygen. The moles of oxygen can then be converted into mass units using the molar mass of oxygen.

Hope this helps!