In a hydrogen molecule, the two hydrogen atoms are held together by a single bond with a bond energy of 436 kj/mol of hydrogen. in other words, to break the h–h bonds in one mole of molecular hydrogen requires the expenditure of 436 kj of energy. using the balanced chemical equation for the formation of water from oxygen and hydrogen (shown above), and interpreting the stoichiometric coefficients as mole amounts, how much energy must be expended in breaking the h–h bonds?

873 kJ of energy will be required to break two moles of hydrogen gas.

Above chemical equation shows that two moles of hydrogen gas is reacting with one mole of oxygen gas to give two mole of water molecule.

Bond energy of H-H = 436kJ

According to reaction we have two moles hydrogen,so energy required to break the

H-H bond in two moles of hydrogen gas will be:

= 872kJ

872kJ of energy will be required to break H-H bond in two moles of hydrogen gas.

answer is: c. the experiment shows that the red substance experienced a chemical change.

this is chemical change (chemical reaction), because two new substances are formed (metalig liquid and gas), the atoms are rearranged and the reaction is followed by an energy change.

this is example of chemical decomposition.

chemical decomposition (analysis) is the separation of a single chemical compound into its two or more elemental parts or to simpler compounds.  

chemical decomposition is opposite of chemical synthesis.

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