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Chemistry Chapter 6

Chemistry Chapter 6. Chemical Reactions and Equations. Chemical Equations. Recognizing Chemical Reactions Change in Color Change in Odor Precipitation (can be a solid from a liquid) Energy changes (heat, light, cools) Evolution of a gas (bubbles)

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Chemistry Chapter 6

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  1. Chemistry Chapter 6 Chemical Reactions and Equations

  2. Chemical Equations • Recognizing Chemical Reactions • Change in Color • Change in Odor • Precipitation (can be a solid from a liquid) • Energy changes (heat, light, cools) • Evolution of a gas (bubbles) Any of these, alone or in combination indicate a reaction has occurred. D. Shepherd NAHS

  3. Writing Chemical Equations • The substances that a reaction begins with are written on the left, they are the REACTANTS • The substances that the reaction ends with are written on the right, they are the PRODUCTS • The two sides are separated by an arrow D. Shepherd NAHS

  4. Word Equation A word equation is a description of what is happening during a chemical reaction. Acetic acid + Sodium hydrogen Carbonate => Sodium acetate + water + carbon dioxide Chemical Equation Uses the actual chemical formulas for each reactant and product. HC2H3O2 + NaHCO3 => NaC2H3O2 + H2O + CO2 Writing Chemical Equation D. Shepherd NAHS

  5. Energy and Equations • Energy can be given off in a chemical reaction – EXOTHERMIC • Energy can be absorbed in a chemical reaction – ENDOTHERMIC • Energy can be in the form of heat or light D. Shepherd NAHS

  6. Law of Conservation of Mass • Matter can’t be created nor destroyed • What is on one side of a chemical equation, must be accounted for on the other side (or the right and left side elements must total exactly the same. • H2 + O2 => H2ODoesn’t add up • 2H2 + O2 => 2 H2ODoes add up • The numbers in front of the elements or compounds are called coefficients and they may only be placed in front of a formula or symbol D. Shepherd NAHS

  7. Types of Reactions • Single Displacement #$ + @ => #@ + $ • Double Displacement #% + $@ => #@ + $% • Synthesis & + # => &# • Decomposition %$ => % + $ • Combustion CXHY + O2 => CO2 + H2O (in this reaction oxygen is always a reactant and Carbon Dioxide and Water are always products.) D. Shepherd NAHS

  8. Nature of Reactions • Reactions are reversible • If energy is given off during a reaction, then energy would need to be put in to get the reaction to go in the opposite direction. • Sometimes reactions go back and forth simultaneously. When the forward and reverse reactions are the same then chemical equilibrium has been reached. D. Shepherd NAHS

  9. Effecting the Rate of Reactions • Temperature - usually an increase in temperature will increase a reaction rate, sometimes the reverse is true, sometimes there is only a “optimum” temperature for the most desirable reaction rate (like those reactions in living things) • Concentration - Raising the concentration will speed up a reaction because there will be more particles to react. D. Shepherd NAHS

  10. Ways to Change Reaction Rates • Adding reactants will speed up a reaction, so will removing products in some cases. • Some reactions require a “push”..this is the activation energy or “energy hill” a reaction must get over to proceed. A spark is that kind of push…then the reaction might continue by itself. Activation energy is different for different reactions. D. Shepherd NAHS

  11. Ways to change reactions • Limiting Reactants (or reagents) – if you are making s’mores and run out of chocolate, then chocolate is the limiting reagent. The same is true for chemical reactions. • Catalysts – speed up reactions, but don’t take part in the reaction themselves. • Inhibitors – slow down reactions D. Shepherd NAHS

  12. Steps in writing chemical equations • Write each element or compound correctly. After you have done this, these formulas or symbols can’t change. • Place the reactants and products on the correct side of the arrow. • Count the number of each kind of atom on each side of the arrow • Use coefficients in front of each reactant or product so that there are the same number and kinds of atoms on each side of the equation. • Add energy to the exothermic side. • Add the states of matter after each substance. (s), (l), (g), (aq). D. Shepherd NAHS

  13. Some Practice with reactions • Zinc metal and Iodine solid are mixed in water. • An aqueous solution of Zinc iodide is produced and heat is given off. • To reverse the reaction, energy must be added. • Write a balanced chemical equation for this reaction. D. Shepherd NAHS

  14. Answer for Zn and I2 • Zn + I2 => Zn I2 + energy (remember that iodine is diatomic) • No coefficients are needed to balance this reaction (one zinc and 2 iodine on each side) • Zn(s) + I2(s) => Zn I2(aq) + energy • Notice the water is not added to the equation. It is implied by the (aq) notation. • This is an example of a synthesis reaction. D. Shepherd NAHS

  15. Single Replacement Reaction • Write an equation for the following reaction. • A copper wire is placed into a solution of Silver Nitrate. The copper replaces the silver to form an aqueous solution of copper nitrate while the silver comes out of solution to form silver metal. D. Shepherd NAHS

  16. Copper/Silver Nitrate Equation • Cu + AgNO3 => Cu(NO3)2 +Ag • Cu + 2AgNO3 => Cu(NO3)2 +2Ag • Cu(s) + 2AgNO3(aq) => Cu(NO3)2 (aq) +2Ag (s) D. Shepherd NAHS

  17. Double Replacement Reaction • Aqueous solutions of Sodium Carbonate and Copper II Chloride react to form Sodium Chloride and Copper II Carbonate. • Write a balanced equation for this reaction. • Na2CO3 + CuCl2 => NaCl + CuCO3 (write compounds) • To find the insoluble product, check the solubility rules on page 821. Add the symbols for the states of each compound. Place coefficients where needed. D. Shepherd NAHS

  18. The Completed Equation • Na2CO3(aq) + CuCl2(aq) => 2NaCl(aq) + CuCO3(s) (carbonates, except those of group 1A are insoluble) • Always make sure to apply the solubility rules in double displacement reactions. • Finally check your work. D. Shepherd NAHS

  19. Synthesis Reaction • One of the simplest synthesis reactions is the formation of sodium chloride from Sodium metal and Chlorine gas. Write a balanced equation for this reaction. • Na(s) + Cl2(g) => NaCl2(s) D. Shepherd NAHS

  20. Decomposition Reaction • Write an equation for the decomposition of Silver oxide to silver metal and oxygen gas. AgO2(s) = Ag(s) + O2(g) D. Shepherd NAHS

  21. Combustion Reaction • Combustion Reactions will always have the following in common: • Oxygen gas will be present on the reactant side • Carbon Dioxide and Water will be present on the products side. • Burning and respiration are examples of Combustion reactions. D. Shepherd NAHS

  22. Combustion Reaction Example • Propane burns completely in air to form Carbon Dioxide and Water. • C3H8(g) + 5O2(g) => 3CO2(g) + 4H2O(g) D. Shepherd NAHS

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