Common Reactions in our Lives Chapter 2 Reactants Products A + B  C + D 2(H 2 )+O 2  2(H 2 O)

Useful Chemical Reaction  What is a chemical reaction? Transformation that occurs when 2 or more substances react together, producing 1 or more new substances with different properties from the original Some common examples:  1) Water is created when hydrogen and oxygen react- one of the keys to life on earth  2) Antacids (magnesium hydroxide-a base) is taken for a stomach ache and neutralizes the hydrochloric acid (an acid) in your stomach  3) Enzymes reacting with carbohydrates to release energy  4) Bleaches contain hydrogen peroxide or sodium hypochlorite, both which contain oxygen that will remove colored stains (O 2 )

Other common reactions…  Swimming pool scents: chlorine is added to water and produces hypochlorous acid, a compound that kills micro-organisms in the pool (Cl 2 )  Baking bread: when flour is mixed with water and yeast, the yeast’s (a micro- organisms) enzymes break down the starch (in the flour) into glucose, the same enzymes then react with the glucose to produce ethanol and Carbon dioxide (CO 2 ) Fermentation: beer and wine making.

Chemical Changes  Chemical reactions are occurring all the time  In a chemical reaction, REACTANTS (=substances found before the reaction) react with eachother and form PRODUCTS (=substances left over after the reaction)  A chemical reaction can be written in a few different ways: example: oxygen reacts with hydrogen to produce water Or, oxygen + hydrogen  water Or, O 2 + 2H 2  2H 2 0

Indicators of Chemical Rxns  During a reaction there are several indicators that show a rxn may have occurred: 1) Gases are given off 2) A new solid or precipitate is formed 3) Color changes 4) Energy is exerted or absorbed (becomes really hot or really cold) 5) Sometimes, odour is given off (BUT NOT ALWAYS!)

Gas fumes kill 3 in Quebec cosmetics factory Last Updated: Monday, July 31, 2006 | 12:36 PM ET CBC News Three people died on the weekend after breathing argon gas in a cosmetics factory at Lac Brome, about 100 kilometres east of Montreal in the Eastern Townships. A 30-year-old Montreal man died Saturday when he was overcome by the gas while welding inside a large metal tank at the factory. A man and a woman who tried to rescue the victim were also overcome by the gas, and died in hospital on Sunday. Argon gas by itself is not toxic, but in an enclosed area it can replace all the oxygen, smothering the victims. The Emballages Knowlton plant produces and packages products such as makeup and shampoo. Quebec's workplace safety board, the coroner and the provincial police are investigating. Safety board spokesman Antoine Tousignant said the welder was not properly equipped for working in a closed space. "It's certain that there was a shortage of safety equipment," Tousignant said. "No accident should occur if all the safety rules are followed." Provincial police Const. Marc Butz said the names of the victims would not be released until he was sure all of the families of the victims had been notified. CBC News

Gases  In many rxns a GAS is produced In the previous slides, CO 2, O 2, and Cl 2 are some examples of common gases produced in rxns. Some tests can be performed to identify gases CO 2 Test O 2 TestH 2 Test ‘Limewater Test’ ‘Reigniting Test’‘POP Test’

Combustion and Neutralization  Combustion: a chemical rxn in which a substance combines with OXYGEN to produce heat and light  Neutralization: an acid is added to a base to produce a new compound and water. The pH of the new compound and water is neutral (7) OR combustion of methanol Note: Phenolphthalein is an pH indicator that is a pinkish color when in the presence of a base and colorless when neutral

Energy and Chemical Rxns  Chemical changes always involve energy changes  Some energy change is noticeable, i.e.-fireworks, while some energy changes are not as obvious i.e.- rusting  2 types of energy changes 1) Exothermic rxn: the release of energy or heat i.e. combustion of gasoline or metabolism (=breakdown of fats, carbs and proteins), Hot packs  The temperature INCREASES 2) Endothermic rxn: the absorption of energy and heat i.e.-in order for photosynthesis to occur, a plant needs to absorb energy from the light  The temperature DECREASES