Chemical Equations & Reactions Chemical Reaction - Study Questions 1. What is a chemical reaction? 2. What is evidence a reaction has occurred? 3. What is a chemical equation? 4. Define reactants. 5. Define products. 6. Define catalyst. 7. What information is found in an equation? 8. What symbols are used to represent the states of matter? 9. What is the meaning of “aq”? 10. How do you indicate a catalyst is being used in a reaction? 11. What is activation energy? 12. What the three things does conservation of matter require of chemical equations? 13. What is the procedure for balancing a chemical equation? 14. Balance the equation for the reaction of magnesium chloride and silver nitrate to form magnesium nitrate and silver chloride. 15. What is a synthesis reaction? 16. How is a combustion reaction related to a synthesis reaction? 17. What type of reaction is an explosion? 18. Compare decomposition and dissociation. 19. What determines whether one metal will replace another in a single displacement reaction? 20. What is the general form of a double displacement reaction? 21. What type of reaction is each of these? 2Na(s) + Cl2(g)  2NaCl(s) PCl5(s)  PCl3(s) + Cl2(g) 2Al(s) + Fe2O3(s)  2Fe(s) + Al2O3(s) C6H12O6(s) + 6O2(g)  6CO2(g) + 6H2O(l) BaCl2(aq) + H2SO4(aq)  2HCl(aq) + BaSO4(s) 22. What is the oxidation number of an element? 23. What is the oxidation number of the fluorine ion? 24. What is the sum of the oxidation numbers in a compound? 31. Can a redox reaction form a molecule? Explain your answer. http://www.unit5.org/chemistry/Equations.html

Describing a Chemical Reaction Indications of a Chemical Reaction Evolution of heat, light, and/or sound Production of a gas Formation of a precipitate Color change Objective: To state four observations that are evidence for a chemical reaction. Photo of precipitate: http://www.geocities.com/chem_reactions/Images/Precipitate.jpg

Signs of Chemical Reactions There are five main signs that indicate a chemical reaction has taken place: release input change in color change in odor production of new gases or vapor input or release of energy difficult to reverse

Chemical Equations Depict the kind of reactants and products aluminum oxide Depict the kind of reactants and products and their relative amounts in a reaction. reactants product 4 Al(s) + 3 O2(g) 2 Al2O3(s) A chemical equation is an expression that gives the identities and quantities of the substances in a chemical reaction Chemical formulas and other symbols are used to indicate the starting material(s) or reactant(s), which are written on the left side of the equation, and the final compound(s) or product(s), which are written on the right side. An arrow, read as yields or reacts to form, points from the reactants to the products. Abbreviations are added in parentheses as subscripts to indicate the physical state of each species:—(s) for solid, (l) for liquid, (g) for gas, and (aq) for an aqueous solution. A balanced chemical equation is when both the numbers of each type of atom and the total charge are the same on both sides. A chemical reaction represents a change in the distribution of atoms but not in the number of atoms. http://img.alibaba.com/photo/10784694/Aluminum_Oxide_Abrasive_Fine_Grit_120_220_.jpg http://upload.wikimedia.org/wikipedia/commons/thumb/f/f2/Corundum_Aluminum_Oxide_Gallantin_Co_MontanaDSC03201.jpg/600px-Corundum_Aluminum_Oxide_Gallantin_Co_MontanaDSC03201.jpg http://www.germes-online.com/direct/dbimage/50327532/Aluminum_Alloy_Pipe.jpg The letters (s), (g), and (l) are the physical states of compounds. The numbers in the front are called stoichiometric coefficients.

4 Al atoms + 3 O2 molecules yield 2 molecules of Al2O3 Chemical Equations aluminum oxide sandpaper 4 Al(s) + 3 O2(g) 2 Al2O3(s) 4 g Al + 3 g O2 yield 2 g Al2O3 This equation means: 4 Al atoms + 3 O2 molecules yield 2 molecules of Al2O3

Chemical Equations Because the same atoms are present in a reaction at the beginning (reactants) and at the end (products), the amount of matter in a system does not change. The Law of Conservation of Matter Kotz web

Chemical Equations Because of the principle of the conservation of matter, An equation must be balanced. It must have the same number of atoms of the same kind on both sides. Lavoisier, 1788

Chemical Equations Reactants – the substances that exist before a chemical change (or reaction) takes place. Products – the new substance(s) that are formed during the chemical changes. CHEMICAL EQUATION indicates the reactants and products of a reaction. Objectives: To identify seven elements that occur naturally as diatomic molecules, H2, N2, O2, F2, Cl2, Br2, I2. [HOBrFINCL twins or BrINClHOF brothers] To write a chemical equation from the description of a chemical reaction. REACTANTS  PRODUCTS

Word Equations A WORD EQUATION describes chemical change using the names of the reactants and products. Write the word equation for the reaction of methane gas with oxygen gas to form carbon dioxide and water. methane + oxygen carbon dioxide + water Reactants Products CH4 + 2 O2 CO2 + 2 H2O

Unbalanced and Balanced Equations H Cl Cl H Cl Cl H H H2 + Cl2  HCl (unbalanced) H2 + Cl2  2 HCl (balanced) reactants products H Cl reactants products H Cl 2 1 2 2 2 1 2 2

Visualizing a Chemical Reaction 2 Na + Cl2 NaCl 2 ___ mole Na 10 10 ___ mole Cl2 5 5 ___ mole NaCl 10 10 ?

Visualizing a Chemical Reaction 2 Na + Cl2 NaCl 2

Meaning of Chemical Formula Symbol Meaning Composition H2O One molecule of water: Two H atoms and one O atom 2 H2O Two molecules of water: Four H atoms and two O atoms H2O2 One molecule of hydrogen peroxide: Two H atoms and two O atoms

Balancing Chemical Equations Balanced Equation – one in which the number of atoms of each element as a reactant is equal to the number of atoms of that element as a product What is the relationship between conservation of mass and the fact that a balanced equation will always have the same number of atoms of each element on both sides of an equation? Objective: To write balanced chemical equations by inspection. Balanced chemical equation – Provides qualitative information about the identities and physical states of the reactants and products – Provides quantitative information because it tells the relative amounts of reactants and products consumed or produced in the reaction – The number of atoms, molecules, or formula units of a reactant or product in a balanced chemical equation is the coefficient of that species – Mole ratio of two substances in a chemical reaction is the ratio of their coefficients in the balanced chemical equation Determine whether the following equation is balanced. 2 Na + H2O  2 NaOH + H2 2 Na + 2 H2O  2 NaOH + H2

CH4 + 2 O2  CO2 + 2 H2O Reactants Products 1 C atom 1 C atom 4 H atoms 4 H atoms 4 O atoms 4 O atoms

Reactants  Products catalyst – speeds up reaction 2 2 Unbalanced

Showing Phases in Chemical Equations H2O(s) H2O(l) H2O(g) Solid Phase – the substance is relatively rigid and has a definite volume and shape. NaCl(s) Liquid Phase – the substance has a definite volume, but is able to change shape by flowing. H2O(l) Gaseous Phase – the substance has no definite volume or shape, and it shows little response to gravity. Cl2(g)

Additional Symbols Used in Chemical Equations “Yields”; indicates result of reaction Used to indicate a reversible reaction A reactant or product in the solid state; also used to indicate a precipitate Alternative to (s), but used only to indicate a precipitate A reactant or product in the liquid state A reactant or product in an aqueous solution (dissolved in water) A reactant or product in the gaseous state (s) (l) (aq) (g)

Additional Symbols Used in Chemical Equations Alternative to (g), but used only to indicate a gaseous product Reactants are heated Pressure at which reaction is carried out, in this case 2 atm Pressure at which reaction is carried out exceeds normal atmospheric pressure Temperature at which reaction is carried out, in this case 0 oC Formula of catalyst, in this case manganese (IV) oxide, used to alter the rate of the reaction D 2 atm pressure 0 oC MnO2