The excess energy which a molecule must posses to become active is known as?

Coefficients

Explanation:

Chemical equations are first written as a skeleton equation, which includes how many atoms each element and compound has. Skeleton equations are not 'balanced' because the number of atoms of each element on the left side (reactants) is not equal to the right side (products).

To balance a chemical equation, you can write coefficients in front of single elements and compounds. The coefficient multiplies with each single element and with each element in the compound.

For example, in this skeleton equation:

H₂ + Cl₂     =>       HCl

Reactants:          Products:

2 hydrogen         1 hydrogen

2 chlorine            1 chlorine

Write the coefficient 2 in the products.

H₂ + Cl₂     =>       2HCl

Now both reactant and product sides have 2 chlorine and 2 hydrogen, so the equation is balanced.