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Chemical Equations & Reactions

Chemical Equations & Reactions. Roman Numerals in Compound Names. Ionic compounds can form from transition metals Transition metals do not always follow the patterns that we discussed Can have more than one oxidation number (charge )

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Chemical Equations & Reactions

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  1. Chemical Equations & Reactions

  2. Roman Numerals in Compound Names • Ionic compounds can form from transition metals • Transition metals do not always follow the patterns that we discussed • Can have more than one oxidation number (charge) • To identify the charges of transition metals, roman numerals are placed in their name, directly after the transition metal • The number of the roman numeral is equal to the charge • You will need to be able to write the formulas of these compounds from their name • I = +1 • II = +2 • III = +3 • IV = +4 • Examples: • Iron (II) chloride • Iron (III) oxide • Fe+2 Cl-1 • FeCl2 • Fe+3 O-2 • Fe2O3

  3. Update SNB p. 11 • On page 11, shade in the following metals in ORANGE and update your key • Then write in their possible charges in each box • 24 Chromium: +2, +3 • 25 Manganese: +2, +3, +4 • 26 Iron: +2, +3 • 27 Cobalt: +2, +3 • 28 Nickel: +2, +3 • 29 Copper: +1, +2 • 30 Zinc: +2 • 47 Silver: +1 • 48 Cadmium: +2 • 50 Tin: +2, +4 • 79 Gold: +1, +3 • 80 Mercury: +1, +2 • 82 Lead: +2, +4

  4. Practice with Roman Numerals Write the formulas of the following compounds: 1. nickel (II) chloride 2. copper (II) nitrate 3. iron (III) hydroxide 4. Gold (I) oxide Ni+2 Cl-1 NiCl2 Cu(NO3)2 Cu+2 NO3-1 Fe+3 OH-1 Fe(OH)3 Au+1 O-2 AuO2

  5. Physical Change • A change in the size, shape, state of matter, etc. that does not change the identityof a substance • A phase change is a physical change even though energy may be removed or added to the substance • In the new state of mater, the substance is still made of the same components, the atoms just have more or less energy (phase changes are the only physical changes that have energy changes) • i.e. if liquid water evaporates, it becomes water vapor if water vapor condenses, it becomes liquid water

  6. Chemical Change • The change of one substance into a new substance (chemical reaction) • A chemical change alters the original chemical make-upof the substance • Energy changes and physical changes always accompany chemical changes

  7. Indications of a Chemical Reaction How can you tell if a chemical change has taken place? • ENERGY Evolution of heat, light, and/or sound (sometimes heat can be absorbed too) • GAS A gas is produced, bubbles (effervescence) • PRECIPITATE When solid particles form from 2 liquids • COLOR – Unexpected Color change (i.e. clear liquid + clear liquid  purple liquid)

  8. Energy • When energy flows out of the system as heat, the process is exothermic. • Usually feels warm • Ex: Combustion of a match, hand warmers • Processes that absorb energy from the surroundings are endothermic. • Usually feels cool • Ex: Melting ice cubes, ice packs

  9. 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 – a description of a chemical reaction that uses chemical formulas and symbols to indicate the reactants and products of a reaction. REACTANTS  PRODUCTS

  10. Additional Symbols Used in Chemical Equations “Produces,” “Forms,” or “Yields”; indicates result of reaction “plus” A reactant or product in the solid state; also used to indicate a precipitate A reactant or product in the liquid state A reactant or product in the gaseous state A reactant or product dissolved in water (in an aqueoussolution) + (s) (l) (g) (aq)

  11. Diatomic Molecules • 7 elements • Molecules made out of 2 atoms (“di” = 2, “atomic” = atoms) • Some elements are never found alone and will always bond with another atom of the same type to become stable (O2, N2, H2, etc.) • Hydrogen and the other 6 elements form a “7” shape (nitrogen has an atomic number of 7) On page 11, shade these 7 elements in YELLOW and add to your key

  12. Chemical Equations Write the equation for the reaction of methane gas (carbon tetrahydride) with oxygen to form carbon dioxide and water. O2 (g) H2O (l) CO2 (g) CH4 (g) + + Reactants Products • Notes: • Water will always be a liquid, unless stated otherwise in the problem • Oxygen is a diatomic molecule and will always be a gas • Carbon dioxide will always be a gas, unless stated otherwise in the problem • If the state of matter is not indicated in the word problem, always assume the element/compound is in it’s normal state at room temperature

  13. Write an equation for the reaction between chlorine and aqueous sodium bromide to produce bromine and aqueous sodium chloride. Cl2 (g)+ NaBr(aq) Br2(l) + NaCl(aq) • Notes: • Chlorine and Bromine are a diatomic molecules • Chlorine is normally a gas at room temperature • Bromine is normally a liquid at room temperature Write the equation for the reaction between solutions of aluminum sulfate and calcium chloride to form a white precipitate of calcium sulfate and aqueous aluminum chloride. Al2(SO4)3(aq)+ CaCl2(aq) CaSO4(s)+ AlCl3(aq)

  14. Solid aluminum oxide is formed when aluminum metal reacts with oxygen. Write the equation for this reaction. Al(s)+ O2 (g) Al2O3(s)

  15. Al(s) + O2(g)Al2O3(s) Counting Atoms 3 4 2 aluminum oxide • The numbers in the front are called coefficients. • Coefficients apply only to the element or compound that comes directly after it. • Just like in math, a coefficient indicates that everything behind it is multiplied by that number • The numbers behind an atomic symbol are called subscripts • Subscripts apply only to the element that comes directly before it • If parenthesis come directly before the subscript, then the subscript is multiplied by everything within the parenthesis • Coefficients and subscripts together – multiply by both the coefficient and subscript 4 Al =4aluminum atoms O2=2oxygen atoms (OH)2=2oxygen atoms 2hydrogen atoms 2(NH4)2=4nitrogen atoms 16hydrogen atoms

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

  17. Chemical Equations Law of Conservation of Matter • Matter is not lost in a chemical reaction- Atoms are just rearranged (Remember John Dalton?) • The same atoms are present in a reaction at the beginning (reactants) and at the end (products) • This means that when we write our chemical equations, we need to have the same number of atoms on both sides of the reaction arrow! Otherwise matter would not be conserved. Kotz web

  18. Cl H H H Cl Cl Cl H reactants products reactants products H H Cl Cl Write the chemical equation for the reaction of hydrogen and chlorine gases to form aqueous hydrogen monochloride. H Cl Cl Cl H H H2(g) + Cl2(g) 2 HCl(aq) (balanced) H2(g) + Cl2(g) HCl(aq) (unbalanced) 2 1 2 2 1 2 2 2

  19. 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 To balance equations, we add coefficientsin front of the element/compound Do notchange the subscripts because then you will change the compound!

  20. Guidelines for Balancing Chemical Equations • Identify the most complex substance. • Beginning with that substance, choose an element that appears in only one reactant and one product. • Adjust the coefficients to obtain the same number of atoms of this element on both sides. • Balance polyatomic ions as a unit (if possible). • Re-write H2O as H-OH if hydroxide is present • 3. Balance the remaining atoms • End with the least-complex substance • Leave single elements/diatomic molecules until last • 4. Double check - Make sure that the atoms of each element are the same on both sides of the equation.

  21. Balancing Equations O2 (g) H2O (l) CO2 (g) CH4 (g) + + 2 2 C = H = O = C = H = O = Cl2 (g)+ NaBr(aq) Br2(g) + NaCl(aq) 2 2 Cl = Na = Br = Cl = Na = Br = Al2(SO4)3(aq) + 3 CaCl2(aq) CaSO4(s) + AlCl3(aq) 3 2 Al = SO4 = Ca = Cl = Al = SO4 = Ca = Cl =

  22. Now you try… 6 2 3 + (NH4)3PO4 + Mg(OH)2 Mg3(PO4)2 NH4OH AlCl3 + Li2CO3  Al2(CO3)3 + LiCl 3 6 2

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