# Limiting and excess reagents

1. May 21, 2007

### ProblemSets

Which of the following is NOT true about limiting and excess reagents?

a.)The amount of product obtained is determined by the limiting reagent.
b.)Some of the excess reagent is left over after the reaction is complete.
c.)A balanced equation is necessary to determine which reactant is the limiting reagent.
d.)The reactant that has the smallest given mass is the limiting reagent

I know that A is true and that B is true for sure. I am not sure about C. To me it seems that I always balance an equation, but maybe that is unneccesary work. My guess though is that because of molar mass, D is not true.

Am i correct?

2. May 21, 2007

### chemisttree

Why would molar mass make D untrue?

3. May 23, 2007

well yes molar mass is important.

example:

if you have 40 grams of hydrogen gas and 50 grams of oxygen gas and you're making water, the balanced equation is 2H2 + O2 -> 2H2O . to find limiting reagent, you need to compare the ratio of the moles you HAVE of reactants to the ratio of moles you NEED to react as far as possible. so to get moles you use molar mass and end up with approximately 20 mol of H2 and 1.6 mol of O2.