Scientific Understanding

**STOICHIOMETRY CONVERSION RATIOS (MOLE TO MOLE RATIOS):**

Many students think stoichiometry is a scary and evil word, but it is just another type of conversion we see in chemistry. Stoichiometry is using the coefficients of a chemical equation to set up a conversion with them. Lets look at an example of what I am talking about with the chemical equation below. Ignore the states of the equation. They are not important in stoichiometry.

N_{2(g)} + 3 H_{2(g)} —-> 2 NH_{3(g)}

From this chemical equation we can state some of the stoichiometry ratios:

What is the ratio between the N_{2} and the H_{2}?

1 N_{2} |

3 H_{2} |

or

3 H_{2} |

1 N_{2} |

What is the ratio between the N_{2} and the NH_{3}?

1 N_{2} |

2 NH_{3 } |

or

2 NH_{3} |

1 N_{2} |

What is the ratio between the H_{2} and the NH_{3}?

3 H_{2} |

2 NH_{3 } |

or

2 NH_{3} |

3 H_{2} |

**VIDEO Stoichiometry Ratios Demonstrated Example 1**: For the chemical equation below what is the ratio of oxygen to H_{2}?

H_{2}SO_{4(aq)} —> H_{2(g)} + S_{(s)} + 2 O_{2(g)}

How do we set up the ratio?

Answer: O_{2} on top and H_{2} on bottom

O_{2} |

H_{2} |

What numbers do we put in front of each?

Answer: The coefficients of each in the chemical equation

COMPLETE ANSWER:

2 O_{2} |

1 H_{2} |

**VIDEO Stoichiometry Ratios Demonstrated Example 2**: For the chemical equation below what is the ratio of H_{2}O to O_{2}?

2 C_{5}H_{7}OH_{(l)} + 13 O_{2(g)} ——> 10 CO_{2(g)} + 8 H_{2}O_{(g)}

How do we set up the ratio?

Answer: H_{2}O on top and O_{2} on bottom

H_{2}O |

O_{2} |

What numbers do we put in front of each?

Answer: The coefficients of each in the chemical equation

COMPLETE ANSWER:

8 H_{2}O |

13 O_{2} |

**PRACTICE PROBLEMS**: Give the stoichiometry (coefficient) ratio for the questions below.

What is the ratio of Fe_{2}O_{3} to FeP?

4 P + 2 Fe_{2}O_{3} ——> 4 FeP + 3 O_{2}

2 Fe_{2}O_{3 } |

4 FeP |

What is the ratio of Al_{2}S_{3} to PbS_{2}?

3 PbS_{2} + 4 AlPO_{4} ——> 2 Al_{2}S_{3} + Pb_{3}(PO_{4})_{4}

2 Al_{2}S_{3 } |

3 PbS_{2} |

What is the ratio of MgO to KF?

MgO + 2 KF ——> MgF_{2} + K_{2}O

1 MgO |

2 KF |

What is the ratio of LiNO_{3} to Ba?

2 Li + Ba(NO_{3})_{2} ——> Ba + 2 LiNO_{3}

2 LiNO_{3 } |

1 Ba |