3 Chemical Reactions-The process by which 1 or more substances undergo change to produce 1 or more different substancesReactions occur when chemical bonds are broken. The atoms rearranged and form new bonds
4 Clues that a reaction has taken place Formation of a gasFormation of a solidColor ChangeEnergy change – heat, cold, light or sound produced
5 Conservation of Energy Chemical reactions involve energyIt takes a certain amount of energy to start the reaction (activation energy)Some reactions release more energy (exothermic)Other reactions absorb energy (endothermic)Energy is conserved just like mass. The energy is always somewhere, in exothermic reactions it is stored in the reactants and then released. In endothermic reactions it is stored in the products.
6 Exothermic Reactions: The energy of the reactants is greater than the products. Energy is released during the reaction in the form of light, heat or electricity.
7 Exothermic Reaction Reactants Products Takes very little activation energy to start the reactionReactants have more energy stored in their bonds than the productsThe extra energy will be released in the form of heat and/or lightExamplesFire, glow stick, foodActivation EnergyReactantsEnergy given offProducts
8 Endothermic Reactions: The energy of the reactants is less than the products. Energy is absorbed (the reaction requires energy to take place)Photosynthesis
9 Endothermic Reaction Products Reactants Takes lots of activation energy to start the reaction (hard to start)Products have more energy stored in their bonds than the reactantsThe extra energy is stored in the bonds of the molecules (like a battery)ExamplesPhotosynthesis (energy absorbed from the sun), photo paper, instant ice packProductsActivation EnergyEnergy stored (absorbed)Reactants
11 Chemical FormulaA shorthand notation for a compound or a diatomic element using chemical symbols and numbers
12 Chemical Formula’sThe formula gives you the names of the elements and tells you how many atoms of each element are in that substance.The small numbers that are written below and to the right of the chemical symbols are called Subscripts, and notes the number of atoms of that element.A number in front of a chemical formula is a coefficient and it is multiplied by the subscript of all the atoms that are in the formula
13 Chemical Formulathe shorthand notation for a compound using chemical symbols and numbersSymbolsSubscript goes with the preceding symbolCoefficientDiatomic moleculesO2N2CompoundsH2OC6H12O6Has 2 oxygen atomsHas 2 nitrogen atomsCO25Has 2 hydrogen atomsand 1 oxygenHas 6 carbon, 12 hydrogenand 6 oxygen atoms
14 Counting Atoms AgNO3 2 MgCl2 Mg (HCO3)2 means 1 Magnesium, 2 Hydrogen, 2 Carbon atoms and 6 Oxygen atomsAgNO3means 1 silver atom, 1 Nitrogen atom and 3 oxygen atoms2 MgCl2means 2 magnesium atoms and 4 chlorine atoms
15 Writing Formulas MgCl2 chloride For example Ionic compounds Magnesium chlorineAlBr3Aluminum bromideIonic compoundsRemember there must be a metal and a nonmetalMetal comes firstAdd “ide” to the end of the nonmetalIgnore the subscriptschloride
16 Examples of ionic compounds (the charges of the ions must be balanced) Lithium fluorideCalcium oxideLithium oxideCalcium fluoridemetalnonmetalmetalnonmetalLiLi+F-FLi+O-2LiFLi2OLiOCharges are balancedCharges are balancedCharges are not balancedmetalnonmetalmetalnonmetalCa+2CaO-2OCa+2F-CaF2CaFCaOCharges are balancedCharges are balancedCharges are not balanced
17 CO2 CH4 H2O Covalent compounds For example Only nonmetals are found Use the prefixes to show the subscripts“Mono” is not used for the first elements in the compoundAdd “ide” to the last nonmetal in the formulaFor exampleCO2Carbon dioxideCH4Carbon tetrahydrideH2ODihydrogen monoxidePrefixesMono Hexa- 6Di- 2 Hepta- 7Tri- 3 Octa- 8Tetra- 4 Nona- 9Penta- 5 Deca- 10Caution: This is a lethal substance (kills thousands of people each year), can be used for rocket fuel, causes billions of dollars in damage, found everywhere
18 Chemical EquationsA shorthand description of a chemical reactions using chemical symbols and formulas.C + O CO2(Yields)ReactantsProducts
19 Balancing Equations + Law of Conservation of Mass Example 2 1 2 Matter is not created or destroyed in ordinary chemical and physical changesThis means that chemical equations must balance.The number and types of atoms that goes into a reaction is the same as what comes out.ExampleHydrogen and oxygen mix to form water.H O H2O212+
20 Equations can only be balanced by changing the coefficient, you can not change a subscript.
21 Balancing Chemical Equations Practice Follow along on your handout as we go through the program.More ReviewINOUT