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Chemical Reactions

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

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Chemical Reactions

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  1. Chemical Reactions Maddie Campbell Zach Dakin Brian Sutton Emily Thompson

  2. 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

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

  4. 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.”

  5. Types of Reactions

  6. Types of Reactions Ctd. Synthesis- 2 or more substances combine to form one substance • 6CO2 + 6H2O = C6H12O6 + 6O2 (Photosynthesis) Decomposition- one substance reacts to form two or more products • Al I3 -> Al + 3I Combustion- the reaction of a substance with oxygen and the release of energy (exothermic) • CH4 + 202 ->CO22H2O • If a flame is produced then combustion is called burning

  7. 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+CuSO4 -> ZnSO4+Cu Double Displacement- elements are exchanged between the reactants • Pb(NO3)2+2KI -> PbI2+2KNO3(also Ionic Precipitation)

  8. Other Reactions Ionic Precipitation- The production of an insoluble solid from the reaction of 2 or more compounds • Pb(NO3)2+2KI -> PbI2+2KNO3(also Double Displacement) Acid-Base Neutralization- in general, the reaction of an acid and a base to produce a salt and water • HCl + NaOH -> H2O + NaCl (also Double Displacement)

  9. 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

  10. Redox Reactions Ctd. Remember OIL RIG! Oxidation Reduction Is the Is the Loss of electrons Gain of electrons

  11. Electrolysis Electrolysis- A reaction in which ions move towards electrodes due to an electrical current • PbBr (l)2 -> Pb(l) + Br2(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

  12. 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

  13. 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

  14. Practice Problems List what type the following reactions are: 1)  NaOH + KNO3 -> NaNO3 + KOH 2)  CH4 + 2 O2 -> CO2 + 2 H2O 3)  2 Fe + 6 NaBr -> 2 FeBr3 + 6 Na 4)  CaSO4 + Mg(OH)2 -> Ca(OH)2 + MgSO4 5)  NH4OH + HBr -> H2O + NH4Br 6)  Pb + O2 -> PbO2 7)  Na2CO3 -> Na2O + CO2 8) What is a physical change? 9) Give two examples of physical changes 10) What is a chemical change (reaction)?

  15. 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.

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