Introduction to Chemical Reactions

1. Introduction toChemical Reactions Types of Chemical Reactions

2. Matter is combined or broken apart to form a new type of matter • Bonds are broken, atoms rearranged, and new bonds are reformed • Chemical reaction is a change in which one or more substances are converted into new substances • The substances that react are called reactants • The new substances produced are called products • This relationship can be written as: Produce Reactants Products Chemical Reactions

3. Release of a gas • Evidence - Bubbles • Change in temperature • Evidence – Temperature goes up (exothermic) • Evidence – Temperature goes down (endothermic) • Change in color • Evidence - solution changes color • Formation of a precipitate • Evidence - forms and settles to the bottom • Energy is released • Evidence - light or sound Evidence (signs) of a Chemical Reaction

4. Symbols Used in Chemical Reactions

5. Reactants • Yield sign • Products • Coefficients • Subscripts HgO(s)  Hg(l) + O2(g) Reactants Products “Yields” Indicates result of reaction Parts of a Chemical Equation

6. Synthesis • Decomposition • Single Replacement • Double Replacement • Combustion Types of Chemical Reactions

7. Generic Form:A + B → AB • Reactants: • A and B are either elements or simple compounds • Products: • AB is a complex compound formed from A and B • Reaction Mechanism: • The atoms of A and B are bonded together to form a single new compound Synthesis Reaction

8. 2 Na + Cl2→ 2 NaCl • Sodium atoms and chlorine gas molecules combine to form a single new product • Sodium chloride is the product of the reaction 2 Mg + O2→ 2 MgO • Magnesium atoms and oxygen gas molecules combine to form a single new product • Magnesium oxide is the product of the reaction • In a moment, we will also see that this reaction can also be classified as a combustion reaction Examples of Synthesis Reactions

9. Generic Form:AB → A + B • Reactants: • AB is a complex compound formed from A and B • Products: • A and B are either elements or simple compounds • Reaction Mechanism: • The compound AB breaks down into its elements or into simple compounds Decomposition Reaction

10. 2 H2O2→ 2 H2O+O2 • Hydrogen peroxide molecules break down to form new products that are simple molecules • Water and oxygen gas are the products of the reaction 2 KClO3→ 2 KCl + 3 O2 • Potassium chlorate molecules break down when heated to form new products that are simple molecules • Potassium chloride and oxygen gas are the products of the reaction Examples of Decomposition Reactions

11. Generic Form:A + O2 → H2O + CO2 • Reactants: • A is a hydrocarbon (a compound of hydrogen and carbon) • O2 is oxygen gas (we will assume more than enough oxygen is present) • Products: • When combusting a hydrocarbon, the products will always be water and carbon dioxide • Reaction Mechanism: • The hydrocarbon is oxidized and produces energy • With a hydrocarbon the reaction is generally rapid Combustion Reaction

12. C2H4 + 3 O2→ 2 CO2 + 2 H2O • Ethene (also known as acetylene) is a hydrocarbon • When O2 is a reactant, the reaction must be combustion • The products must be water and carbon dioxide Examples of Combustion Reactions

13. Generic Form:A + BY → AY + B • Reactants: • A is a metal element • BY is an ionic compound • Products: • AY is an ionic compound • B is a metal element or a diatomic molecule • Reaction Mechanism: • A and B are elements of the same type • If A is more reactive than B, the reaction occurs with A replacing B • If A is less reactive than B, no reaction can occur Single Replacement Reaction

14. 2 Al(s) + 3 CuCl2(aq) → 2 AlCl3(aq) + 3 Cu(s) • Aluminum is a metal and copper is the metal in the ionic compound • Aluminum is more reactive than copper, therefore the reaction occurs • The aluminum replaces the copper ion in the ionic compound and the element copper forms as a precipitate What happens if the reaction is reversed? Cu(s) + AlCl3(aq) → No reaction occurs • The copper is not more reactive than the aluminum, so no reaction occurs Examples of Single Replacement Reactions

15. Generic Form:AX + BY → AY + BX • Reactants: • AX is an ionic compound • BY is an ionic compound • Products: • AY is an ionic compound • BX is a an ionic compound • Reaction Mechanism: • A and B are elements of the same type (both are metals ) as are X and Y (both are non-metals) • A replaces B and X replaces Y (the ions trade partners) • If an insoluble product (precipitate or insoluble gas) is produced, the reaction occurs Double Replacement Reaction

16. Na2SO4(aq) + Ba(NO3)2(aq) → 2 NaNO3 (aq) + BaSO4(s) • The ions in the two ionic compounds change partners and form two new ionic compounds • BaSO4 is not soluble in water • BaSO4 is the product of the reaction What happens if there is no precipitate? Na2SO4(aq) + KNO3 (aq) → No Reaction • The ions of sodium, potassium, sulfate, and nitrate cannot produce an insoluble product • Therefore, there is no product of the reaction and that means there is no reaction between the sodium sulfate and the potassium nitrate Examples of Double Replacement Reactions

17. Types of Chemical Reactions Summary

18. Combustion Reaction - • A + O2 → Oxidized Metal or CO2 + H20 • Decomposition Reaction - • AB → A+ B • Double replacement Reaction - • AX+ BY → AY + BX • Single replacement Reaction - • A + BY → AY + B • Synthesis Reaction - • A+ B → AB Key Terms