Chemical Reactions and Energy Endergonic and Exergonic Reactions

Chemical Reactions & Energy Exchanges All chemical reactions release (lose) or absorb (gain) energy This energy can take the following forms: –Heat –Light –Sound –Electricity Ex: heat produced by a wood fire Ex: Light emitted by a candle Chemical bonds are the source of this energy

More Energy Out Chemical reactions that release energy are called exergonic reactions. –Less energy is needed to break old bonds than to make new bonds…more energy out! –Light or heat is given off –Ex: glow sticks, heat packs

Exothermic Reactions When energy is given off as heat the reaction is called an exothermic reaction. –Burning wood, explosion of dynamite, iron rusting Exothermic reactions provide most of the power for homes and industries. –Fossil Fuels: coal, petroleum, natural gas

More Energy In Chemical reactions that absorb energy are called endergonic reactions. –More energy is needed to break old bonds than to make new bonds…more energy in! –Electricity is often used to supply energy to endergonic reactions –Ex: electroplating metals

Endothermic Reactions When energy is needed in the form of heat the reaction is called an endothermic reaction. –Dissolving Epsom salts in water, cold packs