Chapter 21 Section 4

All chemical reactions release or absorb energy. Energy can take the form of heat, light, sound, or electricity. Chemical bonds are the source of the energy. It is easier to break bonds than to form new bonds. When bonds break you get heat, light, sound, and/or electricity.

An exergonic rxn is one that releases energy. An exothermic rxn is specifically one that produces heat. Exothermic reactions provide most of the power used in homes and industries. Fossil fuels that contain carbon, such as petroleum, coal, and natural gas, combine with oxygen to yield CO2 (g) and energy.

The impurities in those fuels, such as sulfur, burn as well; producing pollutants such as SO2 that then combines with H2O in the atmosphere to produce acid rain.

An endergonic rxn is when it is easier to make new bonds than break the existing bonds so it absorbs energy such as light, heat, or electricity. An enodthermic rxn is one that absorbs heat in order to make new bonds. When you touch this it is cold to the touch. Electricity is the most common form of energy supplied to an endergonic rxn. An example of an endergonic rxn would be electroplating.

Examples of endothermic rxn: Epson salt water bath Barium Hydroxide (BaOH)2 and Ammonium Chloride (NH4Cl) Baking soda and Hydrochloric acid

Catalyst is a substance speeds up a chemical rxn without loosing its own identity. Inhibitor is a substance that prevents a reaction from occurring. *Neither catalysts nor inhibitors change the amount of product produced; they only change the rate of production.*

Why would you consider a log fire to be a exothermic reaction? Why would a catalyst be needed for a reaction? Why do crackers coated with the preservative BHT stay fresh longer than those that aren’t treated? If you wanted to create a product to cool people off would you need an exothermic reaction or an endothermic reaction? Why?