3 A. Describing chemical reactions Chemical Reactions- change of one or more substances converted into new substancesReactants - substances that combine or changeProducts- new substances that are producedproduceReactants Products
4 B. Conservation of MassConservation of Mass-a law which states that, in a chemical reaction, mass is not created or destroyed; it stays the sameAntione Lavoisier – Father of Modern ChemistryFound mass of products equaled the mass of the reactants
5 C. Writing EquationsChemical equation - uses chemical formulas and symbols to describe a chemical reaction and the products it producesChemical formula - expresses the relationship between elements in the compounds and molecules they make upSymbols used to show physical state of reactants; (s) solids (aq) aqueous (g) gas (l) liquid
6 C. Writing EquationsCoefficients – whole numbers in front of the symbol, which represent the number of units of each substance in a reaction **Located before the symbolsSubscripts – small lowered numbers which represent the number of atoms in a molecule of a particular element*Located after and below the symbolsNomenclature – way to name things scientifically
7 Discussion Questions What does the law of conservation of mass state? What is the function of coefficients in a chemical equation?
8 AnswersIn a chemical reaction, matter is neither created nor destroyed. The total sum of the reactants must equal the sum of the product.Chemist need to know how much of a reactant will produce a certain amount of product
9 Describe 3 chemical reactions that you have observed (EX: burning marshmallow) There are many things that let you know it’s a chemical reaction: color change, forming a precipitate, production of heat.
11 Checking for BalanceA balanced chemical reaction- both sides of equation have the same number of atoms of each elementCoefficients are used in front of the element or compound to balance.Choosing coefficients - becomes easier with practice; trial and error at first
12 Writing balanced chemical equations - 4 step process Describe the reaction in wordsWrite the equation using formulas and symbolsCheck for balanceAdd coefficients where needed for balance
13 Discussion QuestionWhy do chemical equations need to be balanced?
14 AnswerLaw of conservation of mass says mass will not be created or destroyed
16 Types of Reactions1. Synthesis Reaction- two or more substance form a new substanceA + B --> AB2. Decomposition Reaction-One substance breaks down into two or more substances AB ---> A + B3. Single-displacement Reaction- one element replaces another one in a compound; A + BC ---> AC +B or D + BC --> BD + C4. Double-displacement Reaction- results if a precipitate, water, or a gas forms when two ionic compounds in a solution are combined; AB + CD --> AD + CB5. Combustion Reaction-a substance combines with oxygen to produce energy“X” + O2 --> CO2 + H2O
17 Oxidation-Reduction (Redox) These reactions often involve oxygenOxidationLoss of electronsSubstance becomes “oxidized”ReductionGain of electronsSubstance becomes “reduced”
18 Discussion Questions1. What two chemical reactions are “opposites” of each other and why?2. What are the 5 types of chemical reactions?
19 Answers Synthesis and decomposition synthesis multiple substances combine to form a new onedecomposition a single substance breaks apart into multiple simpler substancesSynthesis, decomposition, single-displacement, double-displacement, combustion
21 A. Chemical Reactions involve energy exchange Exergonic-Breaking chemical bonds release energyEndergonic-Forming chemical bonds requires energyExothermic-Chemical Reaction where energy is primarily given off in the form of heatEndothermic-Chemical reaction that requires heat energy in order to proceed
22 B. More energy outA catalyst speeds up a chemical reaction without itself being permanetly changedAn inhibitor prevents or slows a chemical reaction or interferes with the catalyst’s action
23 Discussion QuestionHow are chemical bonds involved in energy exchanges?
24 AnswerBreaking bonds release energy; forming bonds to require energy