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Chemical Reactions

Chemical Reactions. Chemical Reactions. Processes in which one or more substances are converted into new substances with different physical and chemical properties Ex: rusted metal, burned toast. Chemical Reactions. Parts of a chemical reaction: Reactants – substances before reaction occurs

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Chemical Reactions

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  1. Chemical Reactions

  2. Chemical Reactions • Processes in which one or more substances are converted into new substances with different physical and chemical properties • Ex: rusted metal, burned toast

  3. Chemical Reactions Parts of a chemical reaction: • Reactants – substances before reaction occurs • Products – substances produced by the reaction

  4. Chemical Reactions Reason why reactions occur: • Increase in stability for products

  5. Types of Reactions • Combination - two substances combine to form new substance • A + B  AB • Ca + Cl2 CaCl2

  6. Types of Reactions • Combustion – substance reacts with oxygen • A + O2 AO • CH4 + O2 CO2 + H2O

  7. Types of Reactions • Decomposition – substance breaks into two or more substances • AB  A + B • MnSO4 MnO + SO3

  8. Types of Reactions • Single-replacement – uncombined element “trades places” with an element in a compound • A +BX  AX + B • Cd + 2 HCl  CdCl2 + H2

  9. Types of Reactions • Double-replacement – two binary compounds “trade partners” • AX +BY  AY + BX • CaCO3 + 2 HCl  CaCl2 + H2CO3

  10. Chemical Equations • Sentences representing a chemical reaction • 2 types • Word equations - gives names of reactants & products • Formula equations – shows chemical formulas and symbols

  11. Chemical Equations • Formula equations… Symbols used: • + reacts/combines with, and •  yields/produces •  precipitate formed •  gas emitted

  12. Chemical Equations • Formula equations… Symbols used: • (s) solid state • (l) liquid state • (g) gaseous state • (aq) aqueous state

  13. Chemical Equations • Diatomic molecule reminder… • Hydrogen H2 • Nitrogen N2 • Oxygen O2 • Fluorine F2 • Chlorine Cl2 • Bromine Br2 • Iodine I2

  14. Chemical Equations Unbalanced Examples: • Calcium reacts with oxygen to produce calcium oxide • Carbon reacts with oxygen to produce carbon dioxide

  15. Chemical Equations Unbalanced Examples: • Solid sodium reacts with chlorine gas to produce solid sodium chloride • Nitrogen gas reacts with hydrogen gas to produce ammonia gas

  16. Chemical Equations Unbalanced Examples: • Sodium hydroxide reacts with hydrogen chloride to produce water and sodium chloride

  17. Chemical Equations Can include heat • Endothermic – heat, from surroundings, enters the system, has positive heat of reaction (DH) value, reactants have lower potential energy than products

  18. Chemical Equations Can include heat Endothermic reaction

  19. Chemical Equations Can include heat Endothermic reaction: • C(s) +2 S(s) + 89.3 kJ  CS2(l) • C(s) +2 S(s) CS2(l) DH = 89.3 kJ

  20. Chemical Equations Can include heat • Endothermic – heat, from surroundings, enters the system • Exothermic – heat exits the system and goes to surroundings, has negative heat of reaction (DH) value , reactants have higher potential energy than products

  21. Chemical Equations Can include heat Exothermic reaction

  22. Chemical Equations Can include heat Exothermic reaction: • CaO(s) + H2O(l)  Ca(OH)2(s) + 65.2 kJ • CaO(s) + H2O(l)  Ca(OH)2(s) DH = -65.2 kJ

  23. Chemical Equations Can include heat • For systems with a constant pressure, heat is also called enthalpy (so DH is also change in enthalpy)

  24. Chemical Equations Can include heat • Enthalpy diagrams – visual representation of a thermochemical equation

  25. Chemical Equations • Enthalpy diagrams – Endothermic reaction

  26. Chemical Equations • Enthalpy diagrams – Exothermic reaction

  27. Chemical Equations How to balance: • Write formula equation with correct formulas & symbols • Count number of atoms on each side of arrow (make table if needed) • Mass must be conserved (number of atoms on each side of arrow are equal), use coefficients to adjust • Work with one atom or ion at a time • Save H & O for last (they tend to be in more than one place & can be difficult) • Recount to ensure that number of atoms are equal on each side

  28. Chemical Equations Balancing examples: • NaOH + HCl  H2O + NaCl • Ca + O2 CaO

  29. Chemical Equations Balancing examples: • N2 + 3 H2 2 NH3 • CH4 + 2 O2 CO2 + 2 H2O

  30. Chemical Equations Balancing examples: • FeCl3 + Na2CO3  NaCl + Fe2(CO3)3 • C2H6 + O2 CO2 + H2O

  31. Chemical Reactions Reaction Rates • Reactions happen if particles have enough energy.

  32. Chemical Reactions Reaction Rates • Factors • Temperature • Concentration • Surface area/Particle Size • Catalysts – substances that speed up reaction without being used

  33. Chemical Reactions Reactions are reversible • When rate of forward and reverse reaction are equal, system is at equilibrium.

  34. Chemical Reactions Reactions are reversible • Equilibrium is described by Le Chatelier’s principle • If stress is applied to a system, the system changes to relieve the stress

  35. Chemical Reactions Reactions are reversible • Factors affecting equilibrium: • Concentration • Temperature • Pressure

  36. Chemical Reactions Reactions are reversible • Equilibrium is described by a constant • Keq, which is a ratio of products to reactants. • Keq > 1, products favored • Keq < 1, reactants favored

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