YEAR 10 CHEMISTRY Chemical Reactions

3 Physical & Chemical Changes What is the difference between a physical and a chemical change? What is the difference between a physical and a chemical change? A physical change is one in which no new substance is formed eg ice melting A physical change is one in which no new substance is formed eg ice melting A chemical change or chemical reaction has occurred if one or more new substances are formed. A chemical change or chemical reaction has occurred if one or more new substances are formed.

PHYSICALCHEMICAL Changes shape A permanent colour change Breaks into smaller pieces A gas is given off Dissolves Change in temperature Mixed with another substance Precipitate forms Changes state One metal is deposited on another No new substances formed New substances are formed

5 Evidence of chemical changes 1. Colour change

6 2. A gas is given off 2. A gas is given off

7 3. Temperature changes Endothermic reactions - absorb heat and as a result the temperature falls Endothermic reactions - absorb heat and as a result the temperature falls Demo Demo Exothermic reactions - release heat and as a result the temperature rises Exothermic reactions - release heat and as a result the temperature rises Demo Demo

8 Endothermic reaction Endothermic reaction of barium hydroxide and an ammonium salt. Endothermic reaction of barium hydroxide and an ammonium salt. Mix the two solids; they react, and the products dissolve in water of hydration. Mix the two solids; they react, and the products dissolve in water of hydration. The reaction feels cold. The reaction feels cold.

9 Exothermic reaction Contains sodium acetate Contains sodium acetate

Metal deposition Sometimes one metal can coat another metal. An example is an iron nail placed in a solution of copper sulfate. The result is an orange coating on the nail. The coating is copper metal. Sometimes one metal can coat another metal. An example is an iron nail placed in a solution of copper sulfate. The result is an orange coating on the nail. The coating is copper metal.

Precipitation When two solutions are mixed, sometimes a solid is formed. The solid is called a precipitate. When two solutions are mixed, sometimes a solid is formed. The solid is called a precipitate.

Chemical Reactions

13 Types of Chemical Reactions There are five types of chemical reactions we will talk about: Synthesis: A + B -> AB Decomposition: AB -> A + B Precipitation: a solid forms Combustion: uses oxygen Single Displacement: A + BC -> AC + B Double Displacement: AB + CD -> AD + CB You need to be able to identify the type of reaction and predict the product(s)

1. SYNTHESIS Synthesis reactions occur when two substances (generally elements) combine and form a compound. Sometimes called combination or addition reactions. In general: A + B  AB reactant + reactant  1 product Example: C + O 2  CO 2

15 1. SYNTHESIS Hydrogen and oxygen yields water Hydrogen and oxygen yields water 2H 2 + O 2  2H 2 O Magnesium plus nitrogen yields magnesium nitride Magnesium plus nitrogen yields magnesium nitride 3Mg + N 2  Mg 3 N 2 Iron and sulfur yields iron(II) sulfide Iron and sulfur yields iron(II) sulfide Fe + S  FeS

Practice Predict the products. Write and balance the following synthesis reaction equations. Sodium metal reacts with chlorine gas Na (s) + Cl 2(g)  Solid Magnesium reacts with fluorine gas Mg (s) + F 2(g)  Aluminum metal reacts with fluorine gas Al (s) + F 2(g) 

2. DECOMPOSITION Decomposition reactions occur when a compound breaks up into the elements or in a few to simpler compounds In general: AB  A + B 1 Reactant  Product + Product Examples: 2H 2 O  2H 2 + O 2 2HgO  2Hg + O 2

2.Decomposition Exceptions Carbonates and chlorates are special case decomposition reactions that do not go to the elements: Carbonates (CO 3 2- ) decompose to carbon dioxide and a metal oxide Example: CaCO 3  CO 2 + CaO Chlorates (ClO 3 - ) decompose to oxygen gas and a metal chloride Example: 2Al(ClO 3 ) 3  2 AlCl O 2 There are other special cases, but we will not explore these

Practice Predict the products. Then, write and balance the following decomposition reaction equations: Solid Lead (IV) oxide decomposes PbO 2(s)  Aluminum nitride decomposes AlN (s) 

Practice Identify the type of reaction for each of the following synthesis or decomposition reactions, and write the balanced equation: N 2(g) + O 2(g)  BaCO 3(s)  Co (s) + S (s)  NH 3(g) + H 2 CO 3(aq) 

21 3. PRECIPITATION Two solutions mixed together make a solid Two solutions mixed together make a solid AgNO 3 (aq) + NaCl (aq) AgCl (s) + NaNO 3 (aq) AgCl precipitate 2 clear solutions reacting to form a yellow precipitate

22 4. COMBUSTION Uses oxygen, happens quickly and produces heat and light. Uses oxygen, happens quickly and produces heat and light.

23 Hydrocarbon combustion reactions What do you notice about these combustion reactions? What do you notice about these combustion reactions? Balance: Balance:

24 5. NEUTRALISATION Acid + base reaction Acid + base reaction Produces salt and water. Produces salt and water. Example: Example: HCl(aq) + NaOH(aq)NaCl (aq) + H 2 O (l)

Amanda Clarke DISPLACEMENT One metal deposits on another. A metal solution reacts to become the pure solid metal. One metal deposits on another. A metal solution reacts to become the pure solid metal. Example: Example: Zn(s) + CuSO 4 (aq)ZnSO 4 (aq) + Cu(s)

Example: When an iron nail placed in a solution of copper sulfate the result is an orange coating on the nail. The coating is copper metal. 6. Single Displacement Fe(s) + CuSO 4 (aq)FeSO 4 (aq) + Cu(s)

27 Classify the following reactions: C 3 H 8 (l) + 5O 2 3CO 2 (g) + 4H 2 O(l) C 3 H 8 (l) + 5O 2 3CO 2 (g) + 4H 2 O(l)Combustion HNO 3 (aq) + LiOH(aq)LiNO 3 (aq) + H 2 O (l) HNO 3 (aq) + LiOH(aq)LiNO 3 (aq) + H 2 O (l)Neutralisation CuSO 4 + 2NaOH(aq)Na 2 SO 4 (aq) + Cu(OH) 2 (s) CuSO 4 + 2NaOH(aq)Na 2 SO 4 (aq) + Cu(OH) 2 (s)Precipitation 2Na(s) + Cu(NO 3 ) 2 2NaNO 3 (aq) + Cu(s) 2Na(s) + Cu(NO 3 ) 2 2NaNO 3 (aq) + Cu(s)Displacement KMnO 4 (s)KMnO 2 (s) + O 2 (g) KMnO 4 (s)KMnO 2 (s) + O 2 (g)Decomposition N 2 (g) + O 2 (g)2NO(g) N 2 (g) + O 2 (g)2NO(g)Combination

Amanda Clarke 2007 Symbols used in Chemical reactions (s) solid (s) solid (l) liquid (l) liquid (g) gas (g) gas (aq) aqueous (a solution: means the substance is dissolved in water) (aq) aqueous (a solution: means the substance is dissolved in water)

Amanda Clarke 2007 Classify the following reactions: C 3 H 8 (l) + 5O 2 3CO 2 (g) + 4H 2 O(l) C 3 H 8 (l) + 5O 2 3CO 2 (g) + 4H 2 O(l)Combustion HNO 3 (aq) + LiOH(aq)LiNO 3 (aq) + H 2 O (l) HNO 3 (aq) + LiOH(aq)LiNO 3 (aq) + H 2 O (l)Neutralisation CuSO 4 + 2NaOH(aq)Na 2 SO 4 (aq) + Cu(OH) 2 (s) CuSO 4 + 2NaOH(aq)Na 2 SO 4 (aq) + Cu(OH) 2 (s)Precipitation 2Na(s) + Cu(NO 3 ) 2 2NaNO 3 (aq) + Cu(s) 2Na(s) + Cu(NO 3 ) 2 2NaNO 3 (aq) + Cu(s)Displacement KMnO 4 (s)KMnO 2 (s) + O 2 (g) KMnO 4 (s)KMnO 2 (s) + O 2 (g)Decomposition N 2 (g) + O 2 (g)2NO(g) N 2 (g) + O 2 (g)2NO(g)Combination

30 Reactants and products Write an equation that shows this experiment. Write an equation that shows this experiment. Indicate the reactants Indicate the reactants Indicate the products Indicate the products

31 Word and chemical equations Word equation Hydrogen + oxygen water Hydrogen + oxygen water Chemical equation 2H 2 + O 2 2H 2 O 2H 2 + O 2 2H 2 O

32 Symbols used in Chemical equations (s) solid (s) solid (l) liquid (l) liquid (g) gas (g) gas (aq) aqueous - the substance is dissolved in water (solution) (aq) aqueous - the substance is dissolved in water (solution)  a gas is given off  a gas is given off ↓ a precipitate forms (a solid in a solution) ↓ a precipitate forms (a solid in a solution)

33 When balancing an equation focus on just ONE element at a time. When balancing an equation focus on just ONE element at a time. Don't try and do it all in your head. Don't try and do it all in your head. Choose an element, balance it and then in the next step worry about how your attempt at balancing has effected other elements. Choose an element, balance it and then in the next step worry about how your attempt at balancing has effected other elements.

34 Balancing chemical equations Na + H 2 O NaOH + H 2 Na + H 2 O NaOH + H 2 This 'equation' is NOT balanced! This 'equation' is NOT balanced! Only place numbers at the front. Only place numbers at the front.