Chemical Properties and Changes Obj: Students will be able to describe a chemical property.

Chemical Changes Chemical Properties –the characteristics of materials that are shown when those materials undergo a chemical reaction. –combination or destruction of compounds a. charges Flammability (will the material combust?) Reactivity—what will the substance react with

Chemical Changes Chemical Change –a change that involves a change in the composition of the substance at the molecular level. –chemical bonds are broken and/or formed –new substances w/new properties are formed –examples: Na + Cl 2 = 2 NaCl –need to balance equation (Law of Conservation of Mass) –Na is a metal that burns in the presence of water, Cl is a toxic gas. H 2 + O 2 = H 2 O

Evidence Recognizing chemical change –Gases are usually given off (fizz, bubble, expand). –Change in color of the substance. –Temperature change, light, and sometimes sound. –Formation of a precipitate (a solid forms within a solution)

Chemical Reactions –Bonds broken and formed –ex. H 2 + O 2 ; break apart; recombine to form H 2 O –new substances with different properties form –no change in total mass

Increasing a Chemical Reaction Concentration the more atoms present, the more atoms there are to react. Surface area surface area increases the reaction surface of a substance. the greater the surface, the faster the reaction.

Cont… Temperature –if atoms gain energy through raising temperature they move quicker and react at a faster rate. Catalyst –a substance that increases the rate of a reaction without being consumed in the reaction.

Chemical Reactions Obj: -students will be able to describe a chemical equation. -students will be able to describe a chemical reaction

Chemical Equations –Represent a chemical reaction. –Symbols are used to represent elements. –Numbers in front of compounds = coefficients (how much of each substance). ex. ( H 2 + O 2  H 2 O) ex. (2 H 2 + O 2  2 H 2 O) Coefficients can be changed. Subscripts cannot be changed!

Chemical Equations Reactants are on left side of the arrow. Products are on the right side Arrow  indicates the yield or produces. –Arrow is treated as the equal sign. Considerations –Bohr Models due Friday –Research assignment from last Thursday is due Friday.

Reaction Examples

Types of Chemical Reactions Types of Chemical Reactions (there are a lot, millions of different reactions). –Scientists classify reactions into several general categories to allow predictions to be made. Synthesis reaction (direct combination) –two or more simpler substances combine chemically to form a more complex substance. –general formula –A + B  AB –Ex. Na + Cl  NaCl

Types of Chemical Reactions Decomposition –a more complex substance breaks down chemically to a simpler substance. –general formula –AB  A + B –Ex. 2H 2 0  2H 2 + O 2 Single Replacement (displacement) –an element will replace another element in a compound, almost always occurs in a solution. – general formula –A + BX  B + AX –Ex. Fe + CuSO 4  Cu + FeSO 4

Examples Decomposition – Synthesis – Single Replacement – Double Replacement – Decomposition – Combustion –

Time Is your sub-atomic particles worksheet turned in? Is your Bohr Model turned in? Have you given your Bohr Model any serious thought?

Types of Chemical Reactions Double Replacement (displacement) a. the anions and cations in two compounds (in solution) change partners. b. general formula –AX + BY  AY + BX –AgNO 3(aq) + NaCl( aq )  AgCl + NaNO 3 –NaCl + KF  NaF + KCl Combustion (burning) a. combustion: rapid reaction of a substance with oxygen. b. general formula –C x H y + O 2  CO 2 + H 2 O –C 3 H 8 + 5O 2  3CO 2 + 4(H 2 O)

Endothermic and Exothermic Reactions

Endothermic/Exothermic Reactions During a chemical reaction, energy is not always completely transferred from reactant to product. Energy can be lost to the surrounding area (exothermic). Reaction can require more energy than the reactants can give, so energy is taken from the surrounding environment. (endothermic).

Endothermic Reactions Endothermic Reaction Reactants have less energy than the products. Energy must be put into the system! These types of reactions “feel cold” because the products require heat energy from their surroundings.

Exothermic Reactions Exothermic Reaction Reactants have more energy than the products. Heat energy is released from the reaction These types of reactions “feel hot” because the products release heat energy into their surroundings.

Endothermic and Exothermic Lab Should have test tube rack and thermometer at your table. Need a baseline reading before both reactions. Sodium Bicarbonate and Hydrochloric Acid (Endothermic) –I scoop of Na(CO 3 ) 2 –one pipette bulbs of 2M HCl acid –Record temp. every 20s for 5 mins Peroxide and Maganese Dioxide (Exothermic) –Record temperature every 20s for 5 mins. –Extremely messy! Hand warmer—in the Styrofoam cup (Exothermic) –Record temperature every 20s for 5 mins. When finished make sure your other assignments are turned in.

Element Research Chose an element from the periodic table. –Perhaps the element you chose for your Bohr model??? Find the following information about the element you chose: –Atomic Number, Atomic Mass, Number of Protons, Number of Electrons, and Number of Neutrons. –Summary (5-7 sentences) of what your element is principally used for. –Relative abundance of your element. –What is the origin of the name of your element? **Don’t use Wikipedia**