Chemical & Physical Changes

Definitions Physical Property: a property that can be seen or measured without changing the identity of the substancePhysical Property: a property that can be seen or measured without changing the identity of the substance –Examples: color, size, density, melting pt Chemical Property: the ability or inability of a substance to react with or change into other substancesChemical Property: the ability or inability of a substance to react with or change into other substances –Examples: flammability, reactivity

5 Signs of a Chemical Change 1.Light being given off 2.Drastic color change 3.Precipitate being formed Precipitate: solid produced during a chemical reaction in a solution 4.Gas given off 5.Change of temperature

Reactions & Equations

I.How do I tell if a reaction has occurred? –A sign of a chemical must take place Temperature change Release of light Color change Appearance of precipitates (solids) Gas/odor released

II.How do I represent a chemical rxn? Reactant 1 + Reactant 2  Product 1 + Product 2 Reactants are starting substances. Products are substances formed. Arrow shows direction of progress. A “+” sign is placed between reactants and products to separate them. Symbols are used to show physical state of reactants and products – (s) solid, (l) liquid, (g) gas, (aq) dissolved in water.

Word & Skeletal Equations A) Word equations: reaction written with words instead of chemical symbols.reaction written with words instead of chemical symbols. Ex. Magnesium (s) + Oxygen (g)  Magnesium oxide (s) Magnesium reacts with oxygen to produce magnesium oxide. B) Skeleton Equations: Use chemical formulas and symbols instead of words – not balanced.Use chemical formulas and symbols instead of words – not balanced. Ex. Mg(s) + O 2 (g)  MgO(s)

Chemical Equations C) Chemical equation: Like skeleton equation but shows conservation of mass – balanced.Like skeleton equation but shows conservation of mass – balanced. Ex. 2Mg(s) + O 2 (g)  2MgO(s)

III.Balancing Chemical Equations We use coefficients in front of reactants and products – usually whole numbers – and tells you the smallest # of particles involved in the reaction.We use coefficients in front of reactants and products – usually whole numbers – and tells you the smallest # of particles involved in the reaction.Steps: 1.Write skeleton equation. 2.Count the # of elements in reaction. 3.Change the coefficients to make the # of atoms of each element equal on both sides of the equation. 4.Write the coefficients in their lowest possible ratio. 5.Check your work.

IV. Conservation of Mass - matter is neither created or destroyed in a chemical reaction. -number of atoms in reactant equals number of atoms in product. -sum of mass in reactant equals sum of mass in product. Ex. Ex. 2H 2 O 2  2H 2 O + O g 32.0g + _?_ 68.0g – 32.0g = 36.0 g

Types of Chemical Reactions

There are five types: 1)Combination 2)Decomposition 3)Single-replacement 4)Double-replacement 5)Combustion

1. Synthesis Generally two or more substances combine to form a single substance.Generally two or more substances combine to form a single substance. General equation: A + B ABGeneral equation: A + B AB EX. Iron and chlorine combine to produce Iron chloride.EX. Iron and chlorine combine to produce Iron chloride. 2Fe (s) + Cl 2 (g)  2FeCl 3 (s)

a. Pb(N0 3 ) 2 + K 2 Cr0 4 PbCr0 4 + KN0 3 b. C1 2 + KI KCl + I 2 c. C 3 H 6 + O 2 CO 2 + H 2 O d. Al(OH) 3 Al 2 O 3 + H 2 O e. Li + O 2 Li 2 O f. HCl + Fe FeC1 3 + H 2 O g. MgC0 3 MgO + CO 2 h. Ba(CN) 2 + H 2 SO 4 BaS0 4 + HCN

2. Decomposition A single compound is broken down into two or more substances.A single compound is broken down into two or more substances. Opposite of synthesis.Opposite of synthesis. General equation: AB A + BGeneral equation: AB A + B EX. Hydrogen peroxide decomposes into water and oxygen.EX. Hydrogen peroxide decomposes into water and oxygen. 2H 2 O 2 (aq)  O 2 (g) + 2H 2 O (l)

a. Pb(N0 3 ) 2 + K 2 Cr0 4 PbCr0 4 + KN0 3 b. C1 2 + KI KCl + I 2 c. C 3 H 6 + O 2 CO 2 + H 2 O d. Al(OH) 3 Al 2 O 3 + H 2 O e. Li + O 2 Li 2 O f. HCl + Fe FeC1 3 + H 2 O g. MgC0 3 MgO + CO 2 h. Ba(CN) 2 + H 2 SO 4 BaS0 4 + HCN

3. Single replacement One element replaces a second element in a compound.One element replaces a second element in a compound. -the more reactive metal will replace the least reactive metal. -the more reactive nonmetal will replace the least reactive nonmetal. General equation: A + BX AX + BGeneral equation: A + BX AX + B EX. 2AgNO 3 (aq) + Cu(s)  2Ag(s) + Cu(NO 3 ) 2 (aq) Silver nitrate reacts with copper to produce silver and copper

a. Pb(N0 3 ) 2 + K 2 Cr0 4 PbCr0 4 + KN0 3 b. C1 2 + KI KCl + I 2 c. C 3 H 6 + O 2 CO 2 + H 2 O d. Al(OH) 3 Al 2 O 3 + H 2 O e. Li + O 2 Li 2 O f. HCl + Fe FeC1 3 + H 2 O g. MgC0 3 MgO + CO 2 h. Ba(CN) 2 + H 2 SO 4 BaS0 4 + HCN

4. Double replacement Involves an exchange of positive ions between two reacting compounds. One of the following applies:Involves an exchange of positive ions between two reacting compounds. One of the following applies: –One product precipitates from solution or –One product is a gas and bubbles out of solution or –One product is a molecular compound such as water. A + X - + B + Y - A + Y - + B + X -A + X - + B + Y - A + Y - + B + X - Ex. AgNO 3 (aq) + NaCl (aq)  AgCl (s) + NaNO 3 (aq)

a. Pb(N0 3 ) 2 + K 2 Cr0 4 PbCr0 4 + KN0 3 b. C1 2 + KI KCl + I 2 c. C 3 H 6 + O 2 CO 2 + H 2 O d. Al(OH) 3 Al 2 O 3 + H 2 O e. Li + O 2 Li 2 O f. HCl + Fe FeC1 3 + H 2 O g. MgC0 3 MgO + CO 2 h. Ba(CN) 2 + H 2 SO 4 BaS0 4 + HCN

5. Combustion An element or compound reacts with oxygen, often producing energy as heat or light.An element or compound reacts with oxygen, often producing energy as heat or light. Important combustion reaction is burning of fossil fuels which produce carbon dioxide and water.Important combustion reaction is burning of fossil fuels which produce carbon dioxide and water. Some synthesis (combination) reaction fall under this category.Some synthesis (combination) reaction fall under this category. Ex. 2Mg(s) + O 2 (g)  2MgO(s)

a. Pb(N0 3 ) 2 + K 2 Cr0 4 PbCr0 4 + KN0 3 b. C1 2 + KI KCl + I 2 c. C 3 H 6 + O 2 CO 2 + H 2 O d. Al(OH) 3 Al 2 O 3 + H 2 O e. Li + O 2 Li 2 O f. HCl + Fe FeC1 3 + H 2 O g. MgC0 3 MgO + CO 2 h. Ba(CN) 2 + H 2 SO 4 BaS0 4 + HCN

Reactions in Aqueous solutions - A solution contains a solute dissolved in water – water is the solvent in most cases. I.Aqueous solutions: Compounds that are soluble in water dissolved into their ions.Compounds that are soluble in water dissolved into their ions. NaCl(aq)  Na + + Cl - see next slide.NaCl(aq)  Na + + Cl - see next slide.

Water molecules surrounding ions. Positive end of water (H) Negative end of water (O)

II. Net ionic equations: 1.Write the chemical balanced equation. 2.If there are ionic compounds solubility rules and determine which chemical compounds are either soluble or insoluble. 3.If they are soluble you should write (aq) after them and if they are insoluble write (s). 4.Rewrite the equation by breaking up the soluble ionic compounds into their ions – remembering to keep the number appropriate with coefficients in front. Do not break up molecular compounds. 5.Cancel out the ions that appear on both sides of the product sign  6.Rewrite the equation again with only the ions that have not been canceled, the solids (insoluble), and molecular compounds. (Net Ionic Equation)

Example 1: silver nitrate + sodium chloride  silver chloride + sodium nitrate 1.AgNO 3 + NaCl  AgCl + NaNO 3 2.soluble soluble insoluble soluble 3. AgNO 3 (aq) + NaCl (aq)  AgCl (s) + NaNO 3 (aq) 4 & 5. Ag + + NO Na + + Cl-  AgCl (s) + Na + + NO Ag+ (aq) + Cl- (aq)  AgCl (s)

You Try…… Barium chloride + sodium sulfate  barium sulfate + sodium chlorideBarium chloride + sodium sulfate  barium sulfate + sodium chloride