First, we should always start with what we're given and what we're trying to find.
We are given that our reactants are Hydrogen (H2) and Oxygen (O2), while our product is H2O.
The chemical equation will look like this:
H2 + O2 --> H2O
However, this isn't balanced. After balancing, we get:
2 H2 + O2 --> 2 H2O
So, we know that we need to produce 90 grams of H2O. How many moles is that? We need to divide by the molar mass (18g) to find out.
90g / 18 g/mol = 5 mol
Great, we need to make 5 moles of water. So, how many times does this reaction need to take place in order to make that? To find this, we need to look at our balanced chemical equation. How many moles of water are produced per reaction? 2 H2 + O2 --> 2 H2O
So, since we make 2 moles of H2O per reaction, how many times does this reaction need to take place? Next, we divide the number of moles that we want by the number of moles created per reaction.
5 moles / 2 moles created per reaction = 2.5 reactions.
Okay, so this reaction needs to take place 2.5 times. Let's go back to the original question, how many moles of hydrogen are required? Again, we look to the balanced chemical equation. How many moles of hydrogen are required per reaction? 2 H2 + O2 --> 2 H2O
So, we know that we need 2 moles of hydrogen per reaction, and we know that this reaction needs to take place 2.5 times. We can simply multiply the two numbers together to find our final answer.
(2 moles of Hydrogen per reaction) * (2.5 reactions) = 5 moles of Hydrogen required
