chemistry

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Based on the balanced equation C4H8S + 7O2 = 4CO2 + 4H2O + SO2 calculate the number of H2O molecules formed when 39 C4H8S molecules and 287 O2 molecules react?

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This is a limiting reagent type problem.
Here is a procedure that will work most limiting reagent problems.
1. Write the equation and balance it. You have that.
2. Convert what you have (in this case 39 molecules and 287 molecules) to moles.
a. moles C4H8S = molecules/6.02 x 10^23.
b. moles O2 = molecules O2/6.02 x 10^23.
3a. Using the coefficients in the balanced equation, convert moles C4H8S to moles H2O formed.
3b. Using the same procedure, convert moles O2 to moles H2O.
3c. Likely you will obtain two different answers. The smaller value is always the correct one.
4. Using the smaller value from 3c, conert moles H2O to molecules.
molecules = moles x 6.02 x 10^23 = ??

Actually, there is a much faster way of doing this (using molecules directly and not converting to moles) but it won't work for all limiting reagent problems. Check my work. Post your work if you get stuck.