# Question #fd69e

Aug 4, 2017

The limiting reactant is the flour. You can make five cakes.

#### Explanation:

This problem is an introduction to stoichiometry with limiting reactants, so let's solve it as if it were a chemical problem.

1. Write the balanced chemical equation for the reaction

$\textcolor{w h i t e}{m m m} \text{1 box cake mix + 1 egg + 2 cups flour + 0.5 cup sugar + 3 Tbsp water → 1 cake}$
$\text{Amt:} \textcolor{w h i t e}{m m m m} 6 \textcolor{w h i t e}{m m m m m l} 12 \textcolor{w h i t e}{m m m m l l} 10 \textcolor{w h i t e}{m m m m m m} 10$
$\text{Divide by:} \textcolor{w h i t e}{m l} 1 \textcolor{w h i t e}{m m m m m m} 1 \textcolor{w h i t e}{m m m m m} 2 \textcolor{w h i t e}{m m m l m m m} 0.5$
$\text{Moles rxn:} \textcolor{w h i t e}{m l} 6 \textcolor{w h i t e}{m m m m m l} 12 \textcolor{w h i t e}{m m m m m} 5 \textcolor{w h i t e}{m m m m m m l} 20$

2. Identify the 'limiting reactant'

An easy way to identify the limiting reactant is to calculate the 'moles of reaction' each will give.

A mole of reaction is just a reaction that has the same moles of each reactant as its corresponding coefficient in the balanced equation.

To get the moles of reaction, you divide the amount ('moles') of each 'reactant' by its corresponding coefficient in the balanced equation.

I did that for you in the table above.

The last line tells you that you have enough

• cake mix for six moles of reaction
• eggs for twelve moles of reaction
• flour for five moles of reaction
• sugar for twenty moles of reaction

The limiting reactant is the substance that gives the fewest moles of reaction.

Here, flour is the limiting reactant because it gives the fewest moles of reaction.

3. Calculate the number of cakes

$\text{Number of cakes" = 10 color(red)(cancel(color(black)("cups flour"))) × "1 cake"/(2 color(red)(cancel(color(black)("cups flour")))) = "5 cakes}$