### All College Chemistry Resources

## Example Questions

### Example Question #21 : Reactions

Consider the unbalanced equation for the combustion of pentane:

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

**Possible Answers:**

**Correct answer:**

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 #1 : General Topics

Consider the following unbalanced reaction:

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

**Possible Answers:**

**Correct answer:**

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 #1 : Stoichiometric Calculations And Dimensional Analysis

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

**Possible Answers:**

**Correct answer:**

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 #21 : Reactions

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

Use the relations , molar mass , and

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