Final answer:
The composition of the chemicals involved in a reaction is the factor that most affects how much chemical energy you start with.
Step-by-step explanation:
The factor that most affects how much chemical energy you start with is the composition of the chemicals involved in the reaction. .
Different chemicals have different amounts of potential energy, and this potential energy depends on their composition.
The composition of the chemicals determines the amount of chemical potential energy present at the start of the reaction.