What is the first step in balancing a redox reaction by the half-reaction method?

First step is to balance the amount of atoms on each side

So for example if my equation that I have to balance is : Br2 -> Br-

First thing I would have to do would be :
Br2 -> 2Br-

Then I would have to balance the charges on both sides. So because there is a -2 charge on the right side I will have to add a -2 charge onto the right side as well. I would do this by :
Br2 + 2e- -> 2Br-

And now you can see the amount of atoms and the charges are balanced... So your overall reaction is now balanced too.

Answer:

a. energy is absorbed in the reaction.

explanation:

if in a given reaction the energy of products is greater than the energy of reactants it means that reaction is endothermic and during the reaction, the energy is absorbed by reactants. in an endothermic reaction, the products have more stored chemical energy than the reactants. and in this reaction the reactants are more stable than products before the compounds with less energy are always more stable.

Heat is involved in chemical change in two ways; chemical changes either result in heat being added to or removed from an object, and chemical changes require a certain amount of heat before they can take place.