College Chemistry : Stoichiometric Calculations and Dimensional Analysis

Study concepts, example questions & explanations for College Chemistry

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Example Questions

Example Question #7 : General Topics

Consider the unbalanced equation for the combustion of pentane:

How many grams of  is required to react with exactly  of .

Possible Answers:

Correct answer:

Explanation:

Start by balancing the given chemical equation:

Next, convert the grams of pentane into moles of pentane.

Use the stoichiometric ratio given by the balanced equation to find the number of moles of oxygen needed to react with the pentane.

Finally, convert the number of moles of oxygen into grams of oxygen.

There should be  significant figures, so the answer is .

Example Question #2 : Stoichiometric Calculations And Dimensional Analysis

Consider the following unbalanced reaction:

How many grams of  can be produced if  of  is mixed with  of ?

Possible Answers:

Correct answer:

Explanation:

Start by balancing the equation:

Next, figure out which reactant is the limiting reactant.

Since fewer moles of  is produced when  is reacted, then  must be the limiting reactant.

Convert the amount of moles of  into grams.

Example Question #8 : General Topics

What is the mass in  of a gas with a volume of  and a density of ?

Possible Answers:

Correct answer:

Explanation:

For this question, we're given the density and volume of a gas and we're asked to find the mass of the gas.

To answer this question, we'll need to use dimensional analysis. What this means is that we'll need to cancel out units in order to obtain the ones that we're looking for.

Example Question #9 : General Topics

Use the equation shown to determine how many grams of water form when  of  reacts completely with  at .

Possible Answers:

 of water

 of water

 of water

 of water

Correct answer:

 of water

Explanation:

Use the relations , molar mass , and

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