Question

C3H8 + 5O2 = 3CO2 + 4H2O
I know this is a combustion reaction but how do you know that the first compounds will produce the nuber of what they did?
Also how do you know that this 2Ca + O2 = 2CaO

Answer 1

It's all based on Mass-Balance. Number of atoms on one side of the equation must appear on the opposite side of the equation.

Answer 2

Can you explain my online lesson really confused me

Answer 3

Sure: let's break apart what each side actually has in it and we'll observe that there are the same number on each side.

C3H8 + 5O2 --> 3CO2 + 4H2O

Let's distribute the coefficients through to the subscripts.

3C + 8H + 10O --> 3C + 6O + 8H + 4O

Combining like terms:

3C + 8H + 10O --> 3C + 8H + (4+6)O

3C + 8H + 10O --> 3C + 8H + 10O

See! The same amounts are on each side!

Answer 4

But how do you get C3H8 + 5O2 --> 3CO2 + 4H2O? I dont understand how that comes out as that? Also, how do you know how it will be ordered? Nothing is making sense

Answer 5

@Mertsj

Answer 6

Well, the order on either side does not matter. That has no significance.

All combustion reactions must produce carbon-dioxide and water. That is the definition of a combustion chemical reaction. Since CO2 and H2O must be produced, you simply balance the reactants to balance with the products.

Answer 7

I still dont get it..... so the product could have a random order.......? Can you give me an example of reactants and explain to me how the product is created through a combustion reaction

Answer 8

What I mean is, how do you know how much oxygen will be burned?

Answer 9

Well you produce water and carbon dioxide simultaneously during the reaction. They are both products and are both formed as a result of combustion.

A combustion reaction in chemistry means that you take a substance, burn it in the presence of oxygen, and you produce water and carbon dioxide. In this case, the substance is C3H8, oxygen is represented by O2, carbon dioxide is CO2, and water is H2O.

Before this equation was written the way it was, it would look like this:

C3H8 + O2 --> CO2 + H2O by the definition of a combustion reaction.

However, notice the amounts of each of the atoms on each side:

3C + 8H + 2O --> 1C + 2O + 2H + 1O

3C + 8H + 2O --> 1C + 2H + 3O

These sides are not equal! They must be in order for the chemical equation to be balanced, so the coefficients are inserted to make the equation true.

C3H8 + "5"O2 --> "3"CO2 + "4"H2O

Answer 10

So none is burned? How do you know what order the substances will make a compound out of?

Answer 11

Sorry, Im slowly figuring this out

Answer 12

Ok I think I understand a little better. Thanks

Answer 13

That's alright :) Chemistry is a pain sometimes.

In the equation above, the coefficients tell how much of each substance is in the reaction. For the combustion reaction we have, we can see that for every 1 mole of C3H8 that is reacted, we burn 5 moles of O2 (just look at the coefficients).

I'm not sure I understand your question about the order of products. In the problem you have here, since it is a combustion reaction, it has to produce water and carbon dioxide. Nothing else. In other types of reactions, obviously the products are based on whatever type of reaction it is.

Answer 14

One thing that might be helpful for you to realize is that others have studied these reactions and typically we are told what reactants produce which products. Once in a while you may be asked to predict the products when you are studying a particular type of reaction. This is not one of those times.

Answer 15

There is a rule of course, called the law of conservation of mass, that the number and type of atoms you start with is the number and type of atoms you will end up with.

Answer 16

So you have to adjust the coefficients to make sure that is true.