law of conservation of mass reactants products diatomic molecule coefficient 8.2 Chemical Equations

Big Idea Ch8 1.In Chemical changes (reactions) atoms are rearranged, never made or destroyed 2.Mass stays the same in chemical changes (reactions) 3. Chemical reactions release energy or absorb energy to break and make chemical bonds

Is matter conserved in chemical reactions? Chemical equations show that in chemical reactions, atoms rearrange, but no atoms are gained or lost. 8.2 Chemical Equations

Conservation of Mass The law of conservation of mass The mass before a chemical reaction is equal to the mass after the reaction. 8.2 Chemical Equations

Chemical Equation Reactants react to produce Products 8.2 Chemical Equations Reactants react to produce Products

Quick check Paper reacts with oxygen to produce carbon dioxide and ashes WHAT ARE THE REACTANTS? WHAT ARE THE PRODUCTS? Is the mass of the paper and oxygen the same as the carbon dioxide, water, and ashes?

Balancing a Chemical Equation Atoms are neither gained nor lost in a reaction, so both sides of the equation must have the same number of atoms. 8.2 Chemical Equations Reactants Products =

Balancing Chemical Equations “Tin + oxygen → tin oxide” reads as “tin plus oxygen produces tin oxide.” To save space let’s use the chemical symbols 8.2 Chemical Equations Sn + O 2 SnO 2 REACTANTS PRODUCTS

Balancing Equations Use the symbols and formulas instead of words. 8.2 Chemical Equations

Elements, Compounds, and Molecules (cont.) 8.2 Chemical Equations

Elements, Compounds, and Molecules (cont.) Some elements are diatomic, that is, they contain two atoms. 8.2 Chemical Equations

Equations for Common Chemical Reactions Reaction of methane: CH 4 + O 2 → CO 2 + H 2 O balance hydrogen CH 4 + O 2 → CO 2 + 2H 2 O balance oxygen CH 4 + 2O 2 → CO 2 + 2H 2 O 8.2 Chemical Equations

Equations for Common Chemical Reactions (cont.) Baking soda and vinegar: NaHCO 3 + HC 2 H 3 O 2 → CO 2 + H 2 O + NaC 2 H 3 O Chemical Equations

Using Parentheses with Formulas When counting atoms inside parentheses, the subscript multiplies all atoms inside. Ca + H 2 O → Ca(OH) 2 + H 2 Ca + 2H 2 O → Ca(OH) 2 + H Chemical Equations

Lesson 2 Review Which is a diatomic molecule? AO2AO2 BH2OBH2O CCH 4 DNDN 8.2 Chemical Equations

Lesson 2 Review What is potassium bromide (KBr)? Aan element Ba mixture Ca compound Da diatomic molecule 8.2 Chemical Equations

Lesson 2 Review In the following equation, which is a reactant? Ca +2H 2 O → Ca(OH) 2 + H 2 AH2AH2 B(OH) 2 CCa Dnone of the above 8.2 Chemical Equations

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8.3Energy and Chemical Change law of conservation of energy exothermic process endothermic process

Conservation of Energy The law of conservation of energy states that energy cannot be created or destroyed, simply changed from one form to another. 8.3 Energy and Chemical Change

Where is the energy from sunlight?

Net Energy During a chemical reaction, reactant bonds are broken and product bonds are formed: –Breaking bonds releases energy. –Forming bonds absorbs energy. –The total of energy in and energy out makes the entire reactions release or absorb energy 8.3 Energy and Chemical Change

Net Release of Energy (cont.) An exothermic process releases energy. The products in an exothermic reaction have less energy than the reactants. 8.3 Energy and Chemical Change

Net Absorbtion of Energy (cont.) An endothermic process absorbs energy. The products in an endothermic reaction have a higher energy than the reactants. 8.3 Energy and Chemical Change

Chemical Bonds Molecules have chemical energy stored in their bonds. Energy is stored in the food that you eat and transferred to your cells. 8.3 Energy and Chemical Change Where is the energy from sunlight? Which is endothermic or exothermic?

Lesson 3 Review Products have a higher energy level than the reactants in an endothermic reaction. AFalse BTrue 8.3 Energy and Chemical Change

Lesson 3 Review ____ bonds ____ energy. ABreaking; releases BBreaking; requires CForming; requires DIonic; release 8.3 Energy and Chemical Change

Lesson 3 Review The law of ____ states that energy is neither created nor destroyed in a chemical reaction. Aconservation of mass Bdefinite proportions Cconservation of matter Dconservation of energy 8.3 Energy and Chemical Change

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Chapter Assessment California Standards Practice Image Bank Science Online Chapter Resources Menu Click on a hyperlink to view the corresponding feature.

Which is a chemical change? Acopper turning green from exposure to air Bdrying clothes Cice melting Dnone of the above Chapter Assessment 1

Which is a chemical property? Aboils at 100°C Bhas a volume of 500 ml Cdoes not rust Dhas a luster Chapter Assessment 2

Which does NOT describe an exothermic reaction? AThere is a net release of energy. BThe reactants have a higher energy than the products. CThe reactants are lower in energy than the products. DThe products are less stable than the reactants. Chapter Assessment 3

What is the coefficient of H 2 O? Ca + 2H 2 O → Ca(OH) 2 + H 2 A1A1 B0B0 C4C4 D2D2 Chapter Assessment 4

How many (OH) molecules are in the products? Ca + 2H 2 O → Ca(OH) 2 + H 2 A1A1 B2B2 C3C3 D4D4 Chapter Assessment 5

In a chemical reaction, which law states the products have the same mass as the reactants? ALaw of Conservation of Water BLaw of Conservation of Energy CLaw of Conservation of Mass DLaw of Conservation of Particles CA Standards Practice 1 SCI 5.b

Energy is ____ in exothermic reactions. Aabsorbed Bcreated Creleased Dstored CA Standards Practice 2 SCI 5.c

If an equation is balanced, the number of atoms in the products is ____ the number of atoms in the reactants. Agreater than Bless than Cequal to Dnone of the above CA Standards Practice 3 SCI 3.b

Which of the following is a physical change? Ahydrogen burning Biron rusting Ccopper turning green when exposed to air Dnone of the above CA Standards Practice 4 SCI X.X

Symbols represent ____ and ____ represent molecules. Aelements; formulas Bformulas; equations Cmolecules; formulas Delements; equations CA Standards Practice 5 SCI 3.f

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