chemistry- stoichiometry limiting and excess exercise

Convert the mass of hydrogen gas into moles of hydrogen gas.
8 grams/ 2 atomic mass units.

= 4mole of hydrogen molecules

4 mole of hydrogen molecules are present to react.

Calculate the mole of water that will be produced from the hydrogen present. Multiply the mole of hydrogen by the ratio.
2/2X 4= 4mole of water.

Calculate the mass of water

Multiply the moles of water by its formula mass.

4 X 18 = 72 grams.

Limiting and excess reactants exercise

Hydrogen reacts with oxygen to form water according to the equation below.

2H₂ + O₂ => 2H₂O

If 8 grams of hydrogen reacts with 128 grams of oxygen what mass of water is formed?
Step 1 Convert to moles all the reactants
Moles of hydrogen = 8 grams/2 atomic mass units = 4mole
Moles of Oxygen gas = 128 grams/ 32 atomic mass units = 4mole

Step 2 Identify the reactant that is the LIMITING reactant. (In other words the reactant that will stop the reaction and the formation of product)
Take hydrogen and ask the following questions.
How much do we have? = 4moles
How much oxygen do we need to react with this amount of hydrogen? = 1/2 X 4moles = 2 mole of oxygen.
Do we have enough ? YES! TOO much, we have 4 mole of oxygen, therefore hydrogen is our limiting reactant.

We now use the hydrogen to work out the mass of water produced.

Double Click anywhere in the green region of the document to see the working out. Click on the squares inside the diagram to reveal more information. Double click to remove the information.

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