The balanced chemical equation for the combustion of hydrogen and oxygen to give

Question

The balanced chemical equation for the combustion of hydrogen and oxygen to give water is 2 H2 + O2 --> 2 H2O

4) Complete the following sentence to describe the number of moles of each reactant involved in the combustion of hydrogen:

___ moles of hydrogen react with ___ moles of oxygen to give moles of water

When the reactants in a mixture are present in the exact mole ratio given by the balanced chemical equation, all of the reactants should be used up when the reaction is over. There will be no “leftover” reactants. However, if one of the reactants is present in an amount greater than its mole ratio, then that reactant cannot react completely, and some of it will be left over at the end of the reaction.

Use the mole ratio of hydrogen to oxygen from question 4 to determine what happens when various hydrogen/oxygen gas mixtures are allowed to burn. Complete the following table to indicate which reactant (H2 or O2) is present in excess, and how much of it will be left over after the combustion reaction is complete. Note: The second one has been completed as an example.

Parts H2

6

5

4

3

2

1

0

Parts O2

0

1

2

3

4

5

6

Which reactant is present in excess?

H2

How much of that reactant is left over?

3

Also, why does oxygen not immediately react with hydrogen during combustion?

Parts H2

6

5

4

3

2

1

0

Parts O2

0

1

2

3

4

5

6

Which reactant is present in excess?

H2

H2

None O2 O2

How much of that reactant is left over?

6

3

N/A 3 6

Explanation / Answer

2 moles of H2 react with 1 mole of O2 to give 2 moles of water.

parts of H2 3 1

Parts of O2 3 5

which reactant present in excess O2 O2

reactant left over 3-1.5 = 1.5 5 - 0.5 = 4.5

[3 part of H2 will reac with 1.5 part of O2. So Here H2 is the limiting reagent.]

The reaction will takes place between reactants when it will overcome the activation energy barrier. Activation enegy depends on the bond enthalpy of H-H and O-O bond. Once it will reach the activation energy reaction will proceed very fast because the reaction is an exothermic reaction. small spark can lead to tha activation of the reaction. That is why oxygen do not immediately react with hydrogen.

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