Chemical & Physical Changes

Definitions Physical Property: a property that can be seen or measured without changing the identity of the substance Examples: color, size, density, melting point Chemical 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 Release of light Drastic color change Formation of precipitate Precipitate: solid produced during a chemical reaction in a solution Gas/odor released Temperature change

Reactions & Equations

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.

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

Conservation of Mass Matter is neither created nor 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. 2H2O2 → 2H2O + O2 68.0g 32.0g + _?_ 68.0g – 32.0g = 36.0 g

Redox Reactions Redox reactions are the transfer of electrons from one reactant to another... When there is oxidation, there is also reduction. The substance which loses electrons is oxidized. The substance which gains electrons is reduced. Rules: The oxidation number is determined by an element in the uncombined state or diatomic elements are Zero (neutral). a monatomic ion & polyatomic ion equals the charge on the ion Oxidized = positive charge (lose electrons) Reduced = negative charge (gained electrons) LEO THE LION GOES GER Lose electrons oxidized, Gained electrons reduced

Let’s Practice: 2Na + FeCl2 → 2NaCl + Fe 2C2H2 + 5O2 → 4CO2 + 2H2O 2PbS + 3O2 → 2SO2 + 2PbO

More Practice….. 2H2 + O2 → 2H2O Cu + HNO3 → CuNO3 + H2 AgNO3 + Cu → CuNO3 + Ag

Single Replacement Reactions and Reactivity

Activity Series A chart of metals listed in order of declining relative reactivity. The top metals are more reactive than the metals on the bottom.

Single replacement 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 + B EX. 2AgNO3 (aq) + Cu(s) → 2Ag(s) + Cu(NO3)2(aq) Silver nitrate reacts with copper to produce silver and copper

Let’s Practice… Cu + 2AgNO3 → 2Ag + Cu(NO3)2 Fe + Cu(NO3)2 → Fe(NO3)2 + Cu Ca + 2H2O → Ca(OH)2 + H2

More Practice… Zn + 2HCl → ZnCl2 + H2 Cl2 + 2NaBr → 2NaCl + Br2 Br2 + 2KI → 2KBr + I2