Unit 8 Chemical Reactions

1. Unit 8 Chemical Reactions

2. What is a Chemical Reaction? • A Chemical Reaction occurs when the chemical composition of a substance changes. • Chemical Reaction: one or more substances are changed into one or more new substances by the reorganization of component atoms.

3. How do chemical reactions occur? The collision theory describes the conditions for a reaction to occur • The collision theory states that particles (atoms or molecules) must collide for a chemical reaction to occur

4. Evidence of a Chemical Reaction • Light is produced • A precipitate (a solid) is formed • Odor/gas is released • Effervescence- bubbling from a gas being produced • Heat and/or a flame is produced • Heat is absorbed • Water is produced • Color change along with another change • The physical/chemical properties of the products are different from the reactants

5. What Evidence of a Chemical Reaction do you see?

6. Chemical Equations • Chemical Equation: A representation of a chemical reaction using the formulas of the starting substances that react and the new substances that are formed • Reactants: the starting substances that enter into a chemical reaction (left side of the reaction arrow) • Products: the new substances formed during a chemical reaction (right side of the reaction arrow) • : yields or a reaction arrow; separates reactants and products X + Y  XY; X and Y are reactants XY is the product

7. Signs and Symbols

8. What symbols are used in writing equations? • Coefficients: Number in front of a substance; apply to all elements in compound/molecule • Subscripts: number after an element; applies to only one element • (g), (l), (s): gas, liquid or solid • (aq): aqueous (dissolved in water)

9. What is the Law of Conservation of Mass? • Matter is neither created nor destroyed in a chemical reaction • The starting mass of reactants = the final mass of products *Must be satisfied when describing a reaction (satisfied by balancing) • Atoms are rearranged • Same number of each element on both sides of the reaction arrow

10. Law of Conservation of Mass • Coefficients: Show amount of each substance. In front of a compound. Apply to all elements in the compound. • Coefficients are used to balance • SUBSCRIPTS CAN NEVER BE CHANGED!!! • H2O: 2 Hydrogen atoms and 1 Oxygen atom • 2 H2O : 4 Hydrogens and 2 Oxygen atoms • Coefficients show proportions of: • Formula units or molecules involved • Relative amounts expressed in moles

11. Balance Chemical Equation • In order for an equation to reflect the Law of Conservation of Mass it must be Balanced. • The # of atoms of each element on the reactants side must equalthe # of atoms of each element on the products side. • A balanced equation has the same number of atoms on BOTH sides of the equation. • Tips to Remember: • NEVER CHANGE THE SUBSCRIPTS when balancing an equation • Must use whole-number coefficients (no fractions) • No coefficient means (1) • If you get stuck, multiple coefficients by 2 and start over (combustion ONLY)

12. Rules for Balancing Equations 1) Write CORRECT formulas for the reactant and product. *Remember the 7 diatomic gases (H2, Br2, O2 N2, Cl2, I2, F2) 2) Balance the number of atoms on both sides by adding coefficients. DO NOT change the subscripts!!!! Useful tips to try: A) Make an element inventory B) Rewrite water as HOH C) Balance polyatomic ions as a group if appear on both sides of the equation D) Balance hydrogen and oxygen last Ex. MgCl2 + H2O  Mg(OH)2 + HCl

13. Practice 2 3 3 • Aluminum sulfate reacts with barium chloride to form aluminum chloride and barium sulfate. • Circle the reactants / underline products • Write the correct formulas for each substance in reaction • Balance the equation. Al2(SO4)3 + BaCl2 AlCl3 + BaSO4

14. Practice • Nitrogen gas plus hydrogen gas under pressure and at high temperature turn into ammonia. • Circle the reactants / underline products • Write the correct formulas for each substance in reaction • Balance the equation. N2 + 3 H22 NH3

15. Five types of Chemical Reactions • Double Displacement- occurs when twodifferent compounds react to form two new compounds. • Single Displacement- occurs when an uncombined element replaces an element that is part of a compound. • Synthesis-occurs when two or more simple substances combine to form one more complex substance. • Decomposition- occurs when one complex substance breaks down into two or more simpler substances • Combustion- a type of double displacement reaction where a compound is reacted/burned with oxygen gas to produce carbon dioxide gas, water, and heat

16. Why are the types of Chemical Reactions important? • Most reactions will fit into one of the five types. (There are exceptions.) • Scientist use the types of reactions to predict products. • Being able to write a chemical equation does not necessarily mean that the reaction will actually take place.

17. What is a Double Displacementreaction? • Two different compounds react to form two new compounds • Also called double replacement • General formula: AX + BY AY + BX • Double displacement reactions: • One of the products formed must be: • A precipitate (a solid) • A liquid (water or will be indicated liquid) • A gas (diatomics or will be indicated gas)

18. Neutralization Reactions A special type of double displacement reaction in which an acid reacts with a base to produce a salt and water

19. Celebrity Double Displacement

20. What are some examples of double displacement reactions? • Ca(OH)2 (aq) + 2HCl (aq) CaCl2 (aq) + 2H2O(l) • 2NaOH(aq) + CuCl2(aq) 2NaCl (aq) + Cu(OH)2 (s) • In each of the reactions one of the products is a solid, liquid, or a gas

21. Solubility • Soluble solid- a solid that readily dissolves in water (aq) • Insoluble solid- a solid that dissolves to such a small degree that it is not detectable to the naked eye (s) • Precipitate- An insoluble solid that forms during a chemical reaction(will look cloudy or look like a solid) (s)

22. Solubility Rules • A set of rules/guidelines that indicate whether a substance will be soluble water (aq) or whether it will be insoluble in water (s) • Located on the back of your periodic table • Know how to use them

23. Soluble or Insoluble? • Sodium Sulfate • Calcium acetate • Fe(OH)2 • AlPO4 • LiOH • PbSO4 • Soluble • Soluble • Insoluble • Insoluble • Soluble • Insoluble

24. Double Displacement Practice • Write and balance the chemical equation for the following reactions. Indicating state of matter. If the reaction will not take place, write NR (for no reaction) after the reaction arrow. • Barium hydroxide reacts with hydrochloric acid to produce barium chloride and water. • Phosphoric acid reacts with ammonium hydroxide to produce ammonium phosphate and water. • Sodium chloride reacts with lithium bromide to form sodium bromide and lithium chloride.

25. What is a Single Displacement reaction? • An uncombined element or a diatomic molecule replaces an element that is part of a compound • Also called single replacement • General formula: A + BX AX + B • Cations will replace cations and anions will replace anions (What type of ions do metals form? What type of ions do non-metals form?) • Requirements: Follow the Activity Series

26. What is the Activity Series? • Arrangement of elements organized in the order of ease with which they undergo certain chemical reactions • Used to predict products for single displacement reactions only • There are two different activity series • Halogens activity series • Metals activity series • Elements can replace any element below it on the activity series, but NOT any element above it

27. Activity Series Halogens Activity Series Metal Activity Series

28. Activity Series for halogens and metals • Activity decreases as you move down the group • Metals Higher on the list will replace metals lower on the list. • A metal lower on the list will not replace a metal above it on the list; in this case we write NR for no reaction • The farther apart 2 elements are on the series, the more likely the higher one will replace the lower one in a compound.

29. Celebrity Single Displacement

30. What are some examples of Single Displacement reactions? • Copper metal reacts with silver nitrate to form silver and copper nitrate Cu(s) + 2 AgNO3(aq) 2 Ag(s) + Cu(NO3)2(aq) • Lithium metal reacts with water to form lithium hydroxide and hydrogen gas 2 Li(s) + 2 H2O (l) 2 LiOH(aq) + H2(g)

31. Reaction or No Reaction? • Ag (s) + Cu(NO3)2 (aq) • F2(g) + 2NaBr(aq) • Br2(g) + NaF(aq) • 2 BN(s) + 3 F2(g)

32. What is a SynthesisReaction? • Occurs when two or more simple substances combine to form one substance that is more complex. *Do not worry about states of matter • General formula is A + B AB • Examples: 2 Fe + 3 Cl22 FeCl3 2 Na + Cl22 NaCl

33. Celebrity Synthesis Reaction

34. Synthesis Reactions Practice Write the complete balanced chemical equation for the following synthesis reactions: • Copper metal reacts with oxygen gas to form copper (II) oxide • Aluminum metal reacts with oxygen gas to form aluminum oxide • Calcium metal reacts with nitrogen gas to form calcium nitride • Solid sulfur (S8) reacts with oxygen gas to form sulfur dioxide

35. What is a DecompositionReaction? • A complex substance breaks down into two or more simpler substances • General formula: AB A + B • Do not worry about states of matter • Examples: • Ammonium nitrate decomposes to form dinitrogen monoxide and water NH4NO3 N2O + 2H2O • Sodium nitride decomposes to form sodium metal and nitrogen gas 2NaN32 Na + 3 N2

36. Celebrity Decomposition Reaction

37. Practice Decomposition Reactions Write the complete balanced chemical equation (including states of matter) for the following synthesis reactions: • Water decomposes into hydrogen gas and oxygen gas • Solid sodium chloride decomposes into sodium metal and chlorine gas • Liquid ammonia decomposes into nitrogen gas and hydrogen gas

38. What is a CombustionReaction? • A type of double displacement reaction in which hydrocarbons (substances made of carbon, hydrogen, and sometimes oxygen) are burned in oxygen to produce carbon dioxide and water vapor • All reactants and products are in the gas state or liquid state • General formula: CxHy (l) + O2 (g) CO2 (g) + H2O (l) • Examples: • CH4(l) + 2O2(g) CO2(g) + 2H2O(l) • 2C2H6(l) + 7O2 (g) 4CO2 (g) + 6H2O(l)

39. Practice Combustion Reaction • Balance the following combustion reactions: Remember Balance hydrogen and oxygen last and if you get stuck, multiple coefficients by 2 and start over (combustion ONLY) ____CH4(g) + ___ O2(g) ____ H2O(g) + ____ CO2(g) ___C12H26(g) + ___ O2(g) ___ H2O(g) + ___ CO2(g) ___C3H8(g) + ____ O2(g) ___ H2O(g) + ___ CO2(g)