1. Unit 5 Chemical Reactions Chemical reactions are changes in matter that produce one or more new substances. Mass is conserved in chemical reactions. Evidence includes – Change in odor – Change in color – Precipitate formation – Gas formation – Release/absorption of heat Reaction rates are influenced by surface area, temperature, and concentration.

2. Chemical Equations Equations show: the reactants that go into the reaction. the products formed. the amounts of each substance used and produced. Some things to remember about writing equations: Diatomic elements are always written Br 2, I 2 N 2, Cl 2, H 2, O 2, F 2 NEVER change a formula (subscript) to balance an equation. Coefficients are used to be sure the same number of atoms of each element are on both sides of the arrow. subscripts

3. Types of Chemical Reactions Synthesis: when two or more simple substances combine to form a more complicated one. + Decomposition: when a complex molecule breaks down to make simpler ones. +

4. Types of Chemical Reactions Single displacement: when one element trades places with another element in a compound. + Double displacement: when the metals (cations) and nonmetals (anions) of 2 compounds switch places, forming two new compounds. +

5. Types of Chemical Reactions Combustion: has oxygen as one of its reactants and carbon dioxide and water as products Acid-Base: acids and bases react to form water and a salt (ionic compound)

6. The Law of Mass Conservation…. The reason we balance equations Mass is conserved in chemical reactions. Matter can neither be created, nor destroyed. Open vs. Closed Systems Closed Systems show mass conservation, while open systems may not.

7. Why use moles? When scientists want to know how many molecules are in a sample of a substance, counting the molecules individually would be completely impractical. Even if you had a way to see the individual molecules, there are just too many, even in a tiny sample. Moles were defined to solve the problem of counting large numbers of molecules. With moles, you count the number of molecules in the sample by weighing it. Think of moles as a "chemist's dozen". Just as 12 eggs is a dozen eggs, 6.02 × 10 23 eggs is a mole of eggs. 6.02 × 10 23 molecules of oxygen is a mole of oxygen. The number of grams in a mole is different from substance to substance. Picture it this way: a dozen elephants have a different weight than a dozen rabbits- but in each case, you have a dozen animals. Similarly, a mole of oxygen gas has a different weight than a mole of water- but in each case, you have 6.02×10 23 molecules. The Mole Concept

8. 3Ag(NO 3 ) + AlCl 3 3AgCl +Al(NO 3 ) 3 3 Moles of Silver Nitrate 1 Mole = Avogadro’s Number = 6.02 x 10 23 Molecules (it’s a unit of measurement…dozen eggs vs. mole of Ag(NO 3 ) How much would a mole weigh?? Molar Mass = atomic mass of the element (ex): Silver has a molar mass of 107.9 g/mole Formula Mass = sum of the molar masses of all the atoms in one molecule of that compound/molecule (ex): Formula Mass of Ag(NO 3 ) = 170 g/mole

9. A mole of any substance is 6.02×10 23 molecules of that substance. You can use this as a conversion factor to turn moles into molecules. and you can go the other way.. A mole of any substance is the molecular weight of that substance in grams. For example, H 2 O has a molecular weight of 18.0 (16.0 for the oxygen and 1.0 for each hydrogen), so the mole-to-gram ratio for water is 1 mole water = 18 g water. You can use this as a conversion factor to turn grams to moles. and, you can go the other way.... 0.001 moles water ×( 6.02×10 23 water ___molecules___ 1 mole water )= 6.02×10 20 water molecules 100 water molecules ×( __1 mole water__ 6.02×10 23 water molecules )= 1.66× 10 -22 moles water 00.0 g water ×( __1 mole water__ 18.0 g water )= 5.56 mole water 6.0 moles O 2 ×( __32.0 g O 2__ 1 mole O 2 )= 192 g O 2

10. Factors that Affect Rate of Reaction Temperature Rate of Reaction Concentration Rate of Reaction PressureRate of Reaction Particle SizeRate of Reaction

11. Factors that Affect Rate of Reaction Catalysts Rate of Reaction Catalysts lower the Activation Energy of reactions. Activation Energy = energy required to start a reaction http://ed.ted.com/lessons/how-to-speed-up-chemical-reactions-and-get-a-date

12. Thermodynamics A chemical reaction always has a change in energy. Bond Energy- energy absorbed as bonds break or released as they form In a reaction either 1) Heat is given out - called Exothermic or 2) Heat is taken in - called Endothermic.

13. Exothermic Reactions If more energy is released than put in, the reaction is exothermic. Exothermic reactions feel warm (energy is released to the surroundings), but the products have less energy than the reactants.

14. Endothermic Reactions If more energy is put in than released, the reaction is endothermic. Endothermic reactions feel cooler (energy is absorbed by the chemicals), but the products contain more energy than the reactants.

15. http://www.quia.com/rr/100887.html?AP_rand=1946970042