# Chemistry

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Total 0/0.5 ...In the explosion of a hydrogen-filled balloon, 0.75 g of hydrogen reacted with 6.9 g of oxygen to form how many grams of water vapor? (Water vapor is the only product.)

i already posted this but i don't think people understood. isnt it because the law of conservation of mass that u just add the grams? but then i tried that and it was wrong. please help!

• Chemistry -

This is a limiting reagent problem and it errs when it states that "0.75 g hydrogen reacts with 6.9 g oxygen" because not all of the oxygen reacts.
Write the equation and balance it.

2H2 + O2 ==> 2H2O

2a. Convert 0.75 g H2 to moles. moles = grams/molar mass.
2b. Convert 6.9 g oxygen to moles the same way.

3a. Using the coefficients in the balanced equation, convert moles hydrogen to moles H2O.
3b. Same procedure, convert moles oxygen to moles H2O.
3c. In limiting reagent problems, the answer for 3a and 3b are not the same; therefore, one of them must be wrong. The correct answer in limiting reagent problems is ALWAYS the smaller one and the reactant producing that value is the limiting reagent.

4. Using the correct answer from 3c, convert mole H2O to grams H2O. moles x molar mass = grams.
I arrived at an answer of about 6.75 g H2O produced but I estimated here and there. You need to confirm that.

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