The following reaction represents the decomposition of hydrogen peroxide

Question

2H2O2 -> o2 (g) + 2H2O (l)

How many molecules of water are produced from the decomposition of 3.4g of Hydrogen peroxide, H2O2?

Please walk me through this one, I need more then just the answer, I need to understand how the work was done. I'm very lost at the moment with this question. Thanks in advance for your help.

Answer 1

Two important things about chemistry.
1. ALWAYS write an equation and balance it.
2. Chemistry works with moles. Therefore, change g to moles first thing you do.

You have the equation. Now change the 3.4 g H2 to moles. moles = grams/molar mass

3.4 g/2.016 = 1.686 moles.

Now using the coefficients in the balanced equation, convert moles H2O2 to moles H2O.
1.686 moles H2 x (2 moles H2O/2 moles H2O2) = 1.686 x (2/2) = 1.686 x (1/1) = 1.686 moles H2O.

Now you know that 1 mole of water is composed of 6.022 x 10^23 molecules. So
1.686 moles H2O x (6.022 x 10^23 molecules H2O/1 mole H2O) = ?? molecules.

Here is a sample stoichiometry problem I've posted. Feel free to use it as needed.
http://www.jiskha.com/science/chemistry/stoichiometry.html