Chemical Reactions ch. 6

Physical Properties melting/boiling points electrical conductivity (metal ions, acids & bases) density color state (solid, liquid, or gas)

Physical Change Changes in physical properties: change of state (melting, evaporation, condensation, freezing) cutting/ripping No change occurs in the identity of the substance

Chemical Change Atoms in substances are rearranged to form one or more different substances Old bonds are broken; new bonds form

Chemical Change Examples: Fe and O 2 form RUST (Fe 2 O 3 ) Baking a cake

Chemical Change Review Signs of a chemical reaction: 1.Color change 2.Gas production (bubbles) 3.Change in temperature 4.Precipitate (formation of a solid) 5.Change in properties

Learning Check Is it a) physical or b) chemical? A.____ a burning candle? B.____ melting ice? C.____ toasting a marshmallow? D.____ cutting a pizza? How’d you do?!?

Chemical Reactions Substances (reactants) rearrange their atoms to form new substances (products) with different physical & chemical properties

Law of Conservation of Mass # & type of Atoms of Reactant(s) MUST EQUAL # & type of atoms of Product(s) Antoine Lavoisier

Chemical Reactions Represented by chemical equations Reactant(s): material(s) that you start out with Product(s): material(s) that you end up with Joined by a yield sign (arrow) ex. 4 Fe + 3 O 2 2 Fe 2 O 3

Synthesis Only one product A + B AB ex. 2 Na + Cl 2 2 NaCl Na ClNa Cl Na ClNa

Decomposition Only one reactant AB A + B ex. 2 H 2 O 2 H 2 + O 2 H O O O HH O HHHHH

Single replacement One element trades places with another in a compound A + BX AX + B Li + NaCl LiCl + Na Li Na Cl Li Cl Na

Double replacement Two elements switch places AX + BY AY + BX NaCl + KF NaF + KCl Na Cl K F Na F K Cl

Other reaction types exothermic reaction: releases heat to surroundings ex. burning (combustion) endothermic reaction: requires heat ex. photosynthesis ex. vinegar & baking soda

Practice! 6K + B 2 O 3  3K 2 O + 2B __________________ HCl + NaOH  NaCl + H 2 O __________________ 4C + S 8  4CS 2 __________________ 2NaCl  2Na + Cl 2 __________________ synthesis single disp. double disp. decomp.

m&m ’s