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Chemical Reactions. Evidence of a Chemical Reaction Energy release (heat or light)

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Presentation on theme: "Chemical Reactions. Evidence of a Chemical Reaction Energy release (heat or light)"— Presentation transcript:

1 Chemical Reactions

2 Evidence of a Chemical Reaction Energy release (heat or light)

3 Evidence of a Chemical Reaction Color change

4 Odor gas bubbles smoke formation

5 Evidence of a Chemical Reaction Precipitation

6 Representing Chemical Equations reactant 1 + reactant 2 → product 1 and product 2 produces Product(s) must be different than the reactants

7 Representing Chemical Equations Simply a “recipe” + + → Eggs and butter and flour produce a cake Word equations name the reactants and products. What is missing from this recipe? AMOUNTS!!!

8 + → Iron (II) and oxygen produce iron oxide Fe (s) + O 2 (g) → FeO (s) What is missing? Amounts! How do you figure out the amounts needed and produced? Representing Chemical Equations

9 Balancing Equations Based on the Law of Conservation of Mass “Matter is not created or destroyed in a reaction, just rearranged.” Fe + O-O → Fe O What is wrong here? an oxygen atom is missing

10 Balancing Equations Atom inventory Fe + O 2 → Fe O Reactant sideProduct side Fe O Fe O Fe + O 2 → Fe O Final equation: Fe + O 2 → Fe O

11 Balancing Equations Steps: 1. Write the skeleton equation (can’t escape formula writing) 2. Count atoms in reactants 3. Count atoms in products 4. Change coefficients to make atom counts match. Never change subscripts. 5. Reduce coefficients if necessary.

12 Practice Problems ____ AlBr3 + ____ K  ____ KBr + ____ Al ____ AlBr3 + 3 K  3 KBr + ____ Al ____ P4 + ____ Br2  ____ PBr3 ____ P4 + 6 Br2  4 PBr3

13 Symbols used in Equations + separates two reactants or two products → “Yields” separated reactants from products (s)Designates a reactant in the solid state (l)Designates a reactant in the liquid state (g) Designates a reactant in the gaseous state (aq) Designates a reactant in the aqueous state → → indicates that heat is supplied to a reaction → Indicates that a catalyst is used (here, platinum)

14 Symbols used in Equations #1 separates two reactants or two products #2 “Yields” separated reactants from products #3 Designates a reactant in the solid state (l)Designates a reactant in the # 4 state (g) Designates a reactant in the # 5 state #6 Designates a reactant in the aqueous state # 7 indicates that heat is supplied to a reaction → Indicates that a # 8 is used (here, platinum) # 9 name the diatomic elements

15 Classifying Chemical Reactions Five general types Synthesis one new product Solid sodium and chlorine gas form solid sodium chloride 2Na(s) + Cl 2 (g) → 2NaCl(s) + →

16 Classifying Chemical Reactions Combustion Must have O 2 as a reactant 2 Mg + O 2 → 2 MgO + → Combustion reactions are exothermic; energy is produced.

17 Classifying Chemical Reactions Combustion of hydrocarbons (compounds containing hydrogen and carbon) CH 4 (g) + 2O 2 (g) → CO 2 (g) + 2H 2 O(g) Most fuels are hydrocarbons

18 Classifying Chemical Reactions Decomposition Only one reactant Hydrogen peroxide decomposes to release oxygen gas and leave water on your skin H 2 O 2(aq) → O 2 (g) + H 2 O (l) 2H 2 O 2(aq) → O 2 (g) + 2 H 2 O (l)

19 Classifying Chemical Reactions Single replacement reactions One reactant is an element Copper reacts with silver nitrate to produce silver and copper nitrate. Cu(s) + AgNO 3 (aq) → Ag(s) + Cu(NO 3 ) 2 (aq)

20 Single replacement reactions Activity Series of Metals LithiumIron RubidiumNickel PotassiumTin CalciumLead SodiumCopper MagnesiumSilver AluminumPlatinum ManganeseGold Zinc

21 Single replacement reactions Halogens Fluorine Chlorine Bromine Iodine

22 Classifying Chemical Reactions Double replacement reactions both reactants are ionic compounds A gas, liquid, or solid must be produced Silver nitrate and sodium chloride react to produce sodium nitrate and silver chloride AgNO 3 (aq) + Na Cl (aq) → NaNO 3 (aq) + AgCl (s) Ag+ Cl - Na+ NO 3 - AgCl Na+ NO3-

23 Summary Reaction Classification Class of ReactionReactantsProbable products SynthesisTwo or more substances One compound CombustionSome substance and oxygen An oxide H 2 0 and CO 2 for hydrocarbon combustion DecompositionOne compoundTwo or more (elements or compounds) Single-replacementAn element and a compound A new compound and the replaced element Double-replacementTwo compoundsTwo different compounds including a s, l, g

24 Reactions in Aqueous Solutions Review: Solution – homogeneous mixture Solute – substance dissolved Solvent – most plentiful substance in the solution Water is the “universal solvent” Other substances can also be solvents

25 Reactions in Aqueous Solutions How does water dissolve ionic compounds? Water is a polar molecule.

26 Reactions in Aqueous Solutions Reactions that form solids Lead nitrate and potassium iodide Two clear solutions – mix – precipitate forms Pb +2 NO 3 - K+I-K+I-

27 Reactions in Aqueous Solutions Reactions that form solids What happened on an atomic level? + → Lead and iodide form a new compound Nitrate and potassium are still dissolved ions – they did nothing but “watch” – spectator ions NO 3 – Pb +2 K+ I- K + NO 3 – PbI 2

28 Reactions in Aqueous Solutions Reactions that form solids Complete ionic equation Pb +2 + NO K + + I - → PbI 2 + NO K + Spectator ions Net ionic equation Pb +2 + I - → PbI 2

29 Reactions in Aqueous Solutions Reactions that form liquids HBr (aq) + NaOH (aq) → H 2 O (l) + NaBr (aq) Complete ionic equation.H + (aq) + Br - (aq) + Na + (aq) + OH - (aq) → H 2 O (l) + Na + (aq) + Br - (aq) Net ionic equation H + (aq) + OH - (aq) → H 2 O (l)

30 Reactions in Aqueous Solutions Reactions that form gases 2HI (aq) + Li 2 S (aq) → H 2 S (g) + 2LiI (aq) Complete ionic equation 2H + (aq) + 2I - (aq) + 2Li + (aq) + S 2- (aq) → H 2 S (g) + 2Li + (aq) + 2I - (aq) Net ionic equation 2H + (aq) + S 2- (aq) → H 2 S (g)


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