Energy Changes in Chemical Reactions
Chemical reactions either release energy (making things hot) or absorb energy (making things cold) - understanding this helps predict what'll happen when chemicals react!
Exothermic reactions release energy to the surroundings, causing temperature increases. Examples include combustion, respiration, and many reactions between acids and metals. Endothermic reactions absorb energy from surroundings, causing temperature decreases - like thermal decomposition or instant ice packs.
Bond energy calculations help predict whether reactions are exothermic or endothermic. Energy is needed to break bonds and released when new bonds form. If more energy is released than absorbed, the reaction is exothermic (ΔH is negative). If more energy is needed than released, it's endothermic (ΔH is positive).
To investigate energy changes practically, you'll measure temperature changes when chemicals react in solution. Use a polystyrene cup (good insulator), measure reactant temperatures first, then monitor how temperature changes during reaction.
Energy rule: Breaking bonds requires energy, making bonds releases energy!