Chemical Reactions Maddie Campbell Zach Dakin Brian Sutton Emily Thompson

Physical Changes A change in physical state Chemical substances don’t change Physical changes are reversible Characteristic properties can be the keys to designing techniques to separate, mix, or reverse physical changes Examples: Adding carrots to a salad, putting ketchup on a burger, melting ice

Chemical Changes: Chemical Reactions Change old substances into different ones Difficult to reverse All chemical reactions involve a change in energy

Energy Changes *The energy change is often in the form of heat energy Endothermic- Net energy change is the addition of energy A melting object gains energy. It is an endothermic energy change. * Although melting ice is a physical change- it involves a phase change of matter, it also is an energy change. It is not usually a chemical reaction. Exothermic- Net energy change is the loss of energy A burning object gives off energy; it loses energy. It is an exothermic energy change. *This is a chemical reaction- see combustion and burning on “Types of Reactions Ctd.”

Types of Reactions

Types of Reactions Ctd. Synthesis- 2 or more substances combine to form one substance 6CO 2 + 6H 2 O = C 6 H 12 O 6 + 6O 2 (Photosynthesis) Decomposition- one substance reacts to form two or more products Al I 3 -> Al + 3I Combustion- the reaction of a substance with oxygen and the release of energy (exothermic) CH >CO 2 2H 2 O If a flame is produced then combustion is called burning

Displacement Displacement- When a more reactive element replaces a less reactive element in a compound Single Displacement- When one element is exchanged between the reactants Zn+CuSO 4 -> ZnSO 4 +Cu Double Displacement- elements are exchanged between the reactants Pb(NO 3 ) 2 +2KI -> PbI 2 +2KNO 3 (also Ionic Precipitation)

Other Reactions Ionic Precipitation- The production of an insoluble solid from the reaction of 2 or more compounds Pb(NO 3 ) 2 +2KI -> PbI 2 +2KNO 3 (also Double Displacement) Acid-Base Neutralization- in general, the reaction of an acid and a base to produce a salt and water HCl + NaOH -> H 2 O + NaCl (also Double Displacement)

Redox Reactions: Oxidation-Reduction Reactions Charges of the elements involved change Always occur in pairs One element loses elections and one element gains electrons ZnO + C -> Zn + CO ZnO has charge, C does not; Zn has no charge, CO does

Redox Reactions Ctd. OxidationReduction Oxidation StateIncrease in oxidation state of an atom or ion Na->Na + Decrease in oxidation state of an atom or ion O->O -2 ElectronsLoss of electronsGain of electrons OxygenGains oxygenLoses oxygen AgentOxidizing Agent- adds oxygen to another substance Reducing Agent- removes oxygen from other substances Cellular ProcessCellular respirationPhotosynthesis Remember OIL RIG!OxidationReductionIs the Loss of electronsGain of electrons

Electrolysis Electrolysis- A reaction in which ions move towards electrodes due to an electrical current PbBr (l) 2 -> Pb(l) + Br 2 (g)l: liquid g: gas Electrolyte- an ionic compound which will conduct electricity when it is molten or dissolved in water; electrolytes will not conduct electricity when solid

Electrolysis Ctd. Cathode- The electrode in any type of cell at which reduction takes place; in electrolysis it is the negative electrode Anode- The electrode in any type of cell at which oxidation takes place; in electrolysis it is the positive electrode Cation- A positive ion which would be attracted to the cathode in electrolysis Anion- A negative ion which would be attracted to the anode in electrolysis Catalyst- A substance which increases the rate of a chemical reaction but itself remains unchanged at the end of the reaction

Signs of a Chemical Reaction Bubbling, effervescence, or production of a gas Formation of a precipitate or solid Change in color Change in temperature Light given off

Practice Problems List what type the following reactions are: 1) NaOH + KNO 3 -> NaNO 3 + KOH 2) CH O 2 -> CO H 2 O 3) 2 Fe + 6 NaBr -> 2 FeBr Na 4) CaSO 4 + Mg(OH) 2 -> Ca(OH) 2 + MgSO 4 5) NH 4 OH + HBr -> H 2 O + NH 4 Br 6) Pb + O 2 -> PbO 2 7) Na 2 CO 3 -> Na 2 O + CO 2 8) What is a physical change? 9) Give two examples of physical changes 10) What is a chemical change (reaction)?

Answers 1) double displacement 2) combustion 3) single displacement 4) double displacement 5) acid-base 6) synthesis 7) decomposition 8) A physical change is a change in physical state; it does not change the chemical substance and is easier to reverse than a chemical reaction. 9) Including, but not limited to: melting ice, adding carrots to a salad, and putting ketchup on a burger 10) A chemical change/reaction changes old substances into new and is very difficult to reverse. It involves a change in energy.