7 Chapter 7.1 Describing Reactions Law of Conservation of Mass –mass cannot be created or destroyed in a chemical equation; it can only change form
8 Chapter 7.1 Describing Reactions In order to show that mass is conserved during a reaction, a chemical equation must be BALANCED (same # of atoms of each element on both sides)Coefficient –number written before the formulaschange these to balance equationNEVER change subscripts
11 Chapter 7.2 Types of Reactions Synthesis –two or more substances react to form a single substance
12 Chapter 7.2 Types of Reactions Decomposition –a compound breaks down into two or more simpler substances
13 Chapter 7.2 Types of Reactions Single Replacement –one element takes the place of another element in a compoundAB + C AC + B p.202
14 Chapter 7.2 Types of Reactions Double Replacement –two different compound exchange positive ions and form two new compoundsAB + CD AD + CB p. 203
15 Models of ReactionsThe following drawings represent reactants and products of three different chemical reactions.1. Synthesis means “putting something together.” Which drawing represents a synthesis reaction? Explain your answer.
16 Models of ReactionsThe following drawings represent reactants and products of three different chemical reactions.2. Decomposition means “taking something apart.” Which drawing represents a decomposition reaction? Explain your answer.
17 Models of ReactionsThe following drawings represent reactants and products of three different chemical reactions.3. Replacement means “something taking the place of another.” Which drawing represents a replacement reaction? Explain your answer.
18 Chapter 7.2 Notes Types of Reactions Other types of Reactions:Combustion –a substance reacts rapidly with oxygen, producing heat and lightOxidation-Reduction (Redox) –electrons are transferred from one reactant to anotherOxidation –process in which an element loses electrons during a chemical reactionReduction –process in which an element gains an electrons during a chemical reaction
19 Chapter 7.2 Notes Types of Reactions Chemical Energy –energy stored in the chemical bonds of a substanceBreaking Bonds = required energyForming Bonds = released energyExothermic Reaction –releases energy to its surrounding – formation of bondsEndothermic Reaction –absorbs energy from its surroundings – breaking of bonds
24 Chapter 7.2 Notes Types of Reactions Law of Conservation of Energy –energy cannot be created or destroyed; it can only change formThe amount of energy in the universe is constant.Activation Energy –The amount of energy required to start a chemical reaction.
25 Chapter 7.3 Notes Types of Reactions Reaction Rate –rate at which reactants change into products over timeFactors that affect reaction rates:1. Temperatureincrease the temperature, the reaction rate will increase; the opposite is also true2. Surface Areaincrease surface area, the reaction rate will increase3. Stirringif you stir something, it will react faster
26 Chapter 7.2 Notes Types of Reactions Factors that affect reaction rates (Cont):4. Concentrationif you increase the concentration, the reaction rate will increase5. Catalyst –speeds up chemical reactions without taking part in the reaction itselfEx) enzymes that speed up digestion6. Inhibitors -slows down or stops chemical reactions from happeningEx) preservatives in foodRates of reaction video
27 Chapter 7.2 Notes Types of Reactions Factors that affect reaction rates (Cont):5. Catalyst –Which reaction requires the least amount of energy to activate?
28 Chapter 7.2 Notes Types of Reactions Equilibrium –a state in which the forward and reverse paths of a change take place at the same ratePhysical equilibrium –both forward and reverse changes occur simultaneouslyEx) water condensing andevaporating at the same rate
29 Chapter 7.2 Notes Types of Reactions Reversible reaction –reaction in which the conversion of reactants into products and the conversion of products into reactants can happen at the same timeChemical equilibrium –forward and reverse chemical changes occur simultaneouslyFactors affecting chemical equilibrium:TemperaturePressureConcentration