chemical equations&reactions

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Chemical Equations & Reaction : 

Chemical Equations & Reaction

Objectives for Section 8-1 : 

Objectives for Section 8-1 List 3 observations that suggest a chemical reaction has taken place List 3 requirements for a correctly written chemical equation Write word & formula equations for a chemical reaction Balance a formula equation

8-1 Describing Chemical Reactions : 

8-1 Describing Chemical Reactions What is a chemical reaction? It is the process by which one or more substances are changed into one or more different substances. The original substances are known as reactants and the resulting substances are known as products.

8-1 Describing Chemical Reactions : 

8-1 Describing Chemical Reactions Indications that a chemical reaction has occurred: 1) Evolution of heat &/or light. 2) Production of a gas. 3) Formation of a precipitate. A precipitate is a solid that is produced as a result of a chemical reaction in a solution that also separates from the same solution.

8-1 Characteristics of Chemical Equations : 

8-1 Characteristics of Chemical Equations What is a chemical equation? It represents with symbols and formulas, the identities and relative amounts of the reactants and products in a chemical reaction.

8-1 Characteristics of Chemical Equations : 

8-1 Characteristics of Chemical Equations Requirements for a correctly written chemical equation: The equation must represent known facts. The equation must contain the correct formulas for the reactants and products. The law of conservation of mass must be satisfied.

8-1 Characteristics of Chemical Equations : 

8-1 Characteristics of Chemical Equations Remember, atoms are neither created nor destroyed. So an equal amount of atoms needs to be represented on both sides of the equation. To equalize the number of atoms you will need to add coefficients where necessary. A coefficient is a small whole number that appears in front of a formula in an equation.

8-1 Word Equations : 

8-1 Word Equations Word equations are those in which the reactants & products are represented by words. methane + oxygen carbon dioxide + water The arrow is read as yields, produces, or forms

8-1 Formula Equations : 

8-1 Formula Equations Formula equations represent the reactants & products by their symbols or formulas. CH4(g) + O2(g) CO2(g) + H20(g)

8-1 Balancing Chemical Equations : 

8-1 Balancing Chemical Equations If given a word equation, convert to a formula equation. Balance the formula according to the law of conservation of mass. This is done by trial and error by adding coefficients. 1) Balance the different types of atoms one at a time. 2) Balance the atoms of elements that are combined that appear only once on each side.

8-1 Balancing Chemical Equations : 

8-1 Balancing Chemical Equations Balance the formula according to the law of conservation of mass. This is done by trial and error by adding coefficients. 3) Balance polyatomic ions that appear on both sides as single units. 4) Balance H & O atoms last.

8-2 Objectives : 

8-2 Objectives Define, give general equations for, & classify: synthesis, decomposition, single replacement, double replacement, & combustion reactions. Predict the products of simple reactions given the reactants.

8-2 Types of Chemical Reactions : 

8-2 Types of Chemical Reactions Synthesis A reaction in which two or more substances combine to form a new substance. A + X AX A & X can be elements or compounds

8-2 Types of Chemical Reactions : 

8-2 Types of Chemical Reactions Synthesis: (A + X AX) 2Mg + O2 2MgO 2Fe + O2 2FeO 2K + I2 2KI

8-2 Types of Chemical Reactions : 

8-2 Types of Chemical Reactions Decomposition A single compound undergoes a reaction that produces two or more simpler substances. AX A + X AX is a compound and A & X can be elements or compounds.

8-2 Types of Chemical Reactions : 

8-2 Types of Chemical Reactions Decomposition: AX A + X 2H2O 2H2 + O2 CaCO3 CaO + CO2

8-2 Types of Chemical Reactions : 

8-2 Types of Chemical Reactions Single Replacement One element replaces a similar element in a compound. A + BX AX + B Or Y + BX BY + X A,B,X,Y are elements. AX, BX, BY are compounds

8-2 Types of Chemical Reactions : 

8-2 Types of Chemical Reactions Single Replacement 2Al + 3Pb(NO3)2 3Pb + 2Al(NO3)2 2Na + 2H2O 2NaOH + H2 Mg + 2HCl H2 + MgCl2

8-2 Types of Chemical Reactions : 

8-2 Types of Chemical Reactions Double Replacement Ions of two compounds exchange places in an aqueous solution to form two new compounds. AX + BY AY + BX A,X,B,Y in the reactants represent ions AY & BX represent ionic or molecular compounds

8-2 Types of Chemical Reactions : 

8-2 Types of Chemical Reactions Double Replacement 2KI + Pb(NO3)2 PbI2 + KNO3 FeS + 2HCl H2S + FeCl2

8-2 Types of Chemical Reactions : 

8-2 Types of Chemical Reactions Combustion A substance combines with OXYGEN, releasing a large amount of energy in the form of heat and light. C3H8 + 5O2 3CO2 + 4H2O The key to recognizing this reaction is that the oxygen compound is alone in the reactants.

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