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Introduction to stoichiometry - Real Chemistry

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Key Questions

  • A very basic intro to stoich...

    video from: Noel Pauller

    Stoichiometry is the calculation of relative quantities of reactants and products in chemical reactions. Stoichiometry is founded on the law of conservation of mass where the total mass of the reactants equals the total mass of the products.

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    C#H_4# + 2#O_2# -----> C#O_2# + 2 #H_2#O

    Here, one molecule of methane reacts with two molecules of oxygen gas to yield one molecule of carbon dioxide and two molecules water. Stoichiometry measures these quantitative relationships, and is used to determine the amount of products/reactants that are produced/needed in a given reaction.

    as per the equation 1 mole of Methane , reacts with 2 moles of Oxygen to produce 1 mole of Carbon dioxide and 2 moles of Water.

    if we double the amount of Methane and Oxygen to 2 moles and 4 moles respectively , the amount of carbon dioxide ad water we will get also get doubled up.

    How many moles of chlorine gas (#Cl_2#) would react with 5 moles of sodium (Na) according to the following chemical equation? (Balance equation.) 2Na + #Cl_2# -----> 2NaCl

    (b) Using the equation (after it is balanced) above, determine the amount of product that can be produced from 24.7 g Na.

    As per the equation 2 moles of sodium produces one mole of #Cl_2# , so the amount of #Cl_2# required is one half the amount of Sodium , Na.
    If we start with 5 moles of Na , we will need 5 / 2 moles or 2.5 moles of #Cl_2#.

    (b) As per the equation 2 moles of sodium ( mass 46 g) produces two moles of NaCl (116.8g)
    we can say 46 g of Na on reaction with sufficient amount of Chlorine produces 116.8 g of NaCl.

    1 g of Na on reaction produces (116.8 / 46 ) g of NaCl

    24.7 g of Na on reaction will produce ( 116.8 / 46 ) x 24.7 g of NaCl

    62 g of NaCl.

  • Answer:

    There are a number of reasons why chemistry students study stoichiometry. I'd say the most important is the ability to make useful predictions.


    Stoichiometry allows us to make predictions about the outcomes of chemical reactions. Making useful predictions is one of the main goals of science, the other being the ability to explain phenomena we observe in the natural world.

    So what kind of predictions can we make using stoich? Here are some examples:

    1. Predict the mass of a product of a chemical reaction if given the starting masses of reactants.
    2. Predict the volume of a gas which will be produced by a reaction if given the starting amounts of reactants.
    3. Determine the optimal ratio of reactants for a chemical reaction so that all reactants are fully used.

    Stoichiometry is also challenging, so there are lessons about work ethic, problem solving techniques and perseverance...

    Stoichiometry gives us the ability to tie together learning about chemical reactions, formulas of compounds, mole calculations and conversions!

    Here is a video which uses the analogy of making sandwiches to introduce the concept of stoichiometric calculations.

    video from: Noel Pauller

    Noel P.

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