Can you help me understand balancing chem equations?

[Surbey]

I have a few questions about balancing chem equations.

I can easily do it when I can see the reactants and products. No problem. But how do I do it when I only have the reactants? How am I supposed to know what the products are??

For example, one of the problems I have is with H2O + Ca. I know that H2O + Ca are the reactants and it is a single replacement reaction. But does this mean that it’s simply H2 + CaO? Is it really that simple?

[Malacandra]

@Surbey

I have a few questions about balancing chem equations.

I can easily do it when I can see the reactants and products. No problem. But how do I do it when I only have the reactants? How am I supposed to know what the products are??

For example, one of the problems I have is with H2O + Ca. I know that H2O + Ca are the reactants and it is a single replacement reaction. But does this mean that it’s simply H2 + CaO? Is it really that simple?

I guess part of the answer is that as a chemist you’re supposed to know how these substances behave when they’re put together. For instance, if you drop a lump of calcium into water, do you get calcium oxide floating around in the water and hydrogen bubbling off?

:dubious:

[glee]

@Surbey

I have a few questions about balancing chem equations.

I can easily do it when I can see the reactants and products. No problem. But how do I do it when I only have the reactants? How am I supposed to know what the products are??

For example, one of the problems I have is with H2O + Ca. I know that H2O + Ca are the reactants and it is a single replacement reaction. But does this mean that it’s simply H2 + CaO? Is it really that simple?

I only have a basic school qualification in Chemistry (and it was 35 years ago :eek: ).

However couldn’t you investigate the quantities of hydrogen being given off, and analyse the remaining compounds?
If you knew that all the hydrogen in the converted water was changed to hydrogen gas, you would know that no other hydrogen compounds were being formed.
And if the remaining compound was only CaO, then you have your equation!

[Lightray]

You just have to know the chemistry you’re dealing with, to understand what the reaction products will be.

In this case, you’ll form calcium hydroxide – Ca(OH)2 – sensibly enough, since you’re adding water (= hydration).

See here for the equations. This site actually has the reaction as a lab demonstration, with pictures.

You’ll notice in the first cite, the comparison of calcium’s reaction with what you’d expect of magnesium’s. Mn is right above Ca on the periodic table. That’s how you can start making guesses that Mn + H2O would probably yield Mn(OH)2; but then you find that Mn is doesn’t react as strongly with water as Ca.

Another way you can guess as to probable reaction products is by knowing the characteristics of those reaction products. CaO hydrates readily (even, violently) in the presence of H2O. So if you’re starting with an aqueous system as with Ca + H2O, you’re not likely to end up with CaO – it’ll immediately hydrate to Ca(OH)2.

So, it is kinda “that simple,” but you have to pare down your guesses at reaction products by what you know of the chemistry. And to do that, you have to know a little more (whether or not it’s provided in the problem you’ve been posed).