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BALANCING EQUATIONS & CHEMICAL REACTIONS

BALANCING EQUATIONS & CHEMICAL REACTIONS. Changes in Energy (E) Release of E as heat Release of E as light Production of sound Reduction or increase of temperature Absorption or release of electrical Energy. Formation of new substances Formation of a gas Formation of a precipitate

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BALANCING EQUATIONS & CHEMICAL REACTIONS

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  1. BALANCING EQUATIONS & CHEMICAL REACTIONS

  2. Changes in Energy (E) Release of E as heat Release of E as light Production of sound Reduction or increase of temperature Absorption or release of electrical Energy Formation of new substances Formation of a gas Formation of a precipitate Change in color Change in odor Evidence of Chemical Change

  3. Conservation of Mass Law of Conservation of Mass • In any physical or chemical reaction, mass is neither created nor destroyed; it is conserved! Reactants Products Same number of atoms on both sides of the equation!

  4. Balancing Equations In every balanced equation each side of the equation has the same number of atoms of each element

  5. Vocab Terms • Subscripts – tells how many atoms of each element you have NH3(one nitrogen, three hydrogen)- DON’T mess with these!! • Coefficients– small whole number that appears in front of a chemical formula in an equation – you get to “mess” with these. 2NH3 (Two molecules of ammonia or two moles of ammonia) •  the arrow means yields or reacts to produce

  6. REACTANTSPRODUCTS You have to get the same number of elements on each side of the reaction

  7. Balancing Rules • Never touch subscripts when balancing equations, you will change the substance • Include all sources of the element CH3CHOOH + NaOH • Polyatomic ions that appear intact on both sides of the equation, can be balanced as a group (PO4) • Coefficientsin your balanced equation contain the lowest possible ratio.

  8. Balancing! Aluminum + Oxygen  Aluminum Oxide Al + O2 Al2O3 Until you get good at this, it is helpful to write the number of atoms of each element on both sides of the equation. It helps you to keep track of the atoms.

  9. Balancing! Ethene + Oxygen  Carbon Dioxide + water C2H4+ O2 CO2 + H2O

  10. Balancing! Hydrogen gas + nitrogen gas  ammonia Remember your diatomic molecules!!!

  11. Try this one! NaNO3 + CrCl3 NaCl + Cr(NO3)3

  12. Balance this equation… NaNO3 + CrCl3 NaCl + Cr(NO3)3 Write the word equation.

  13. Four abbreviations are used to indicate physical states of chemicals:shown as subscripts in the chemical equation (s) = solid (l) = liquid (g) = gas (aq)= aqueous solution (dissolved in water) Symbols over the arrow indicate the conditions of the reaction Heat Pressure Temperature Catalyst Reversible reaction Important stuff!

  14. Why does it happen? Use the file to make four hash marks perpendicular to the face of the penny. Carefully drop the penny into the 6M HCl solution.

  15. Check out the Pennys! Make some qualitative observations about the pennies. (Look at the dates- remember what you learned at the beginning of the year in the Penny Density Lab) As we proceed: You may want to write these down! • What kind of reaction • Write and balance the chemical equation. • Explain your observations. • What kind of quantitative observations would be helpful?

  16. Warm Up- A sample contains a compound with 3.60 g of carbon and 0.61 g of hydrogen. The molar mass of the compound is 42.09g/mol. Determine the formula of the compound. Remind me to pass back your EMP Formula Packets. I only graded a few- answers are posted on line.

  17. Wonder Projects- HONORS ONLY Go to my website

  18. REACTIONS

  19. Combination Reactionor Synthesis Reaction • Two or more simple substances react to form a more complicated one A + B  AB Fe + S  FeS

  20. Combination Reactions We can predict the products of ionic compounds by thinking about the charge! Ga (s) + O2 (g)  Cu (s) + S(s)  Are there 2 possible products to the 2nd reaction? How would we “say” these equations?

  21. Decomposition Reaction • A decomposition reaction is the opposite of a composition reaction - a complex molecule breaks down to make simpler ones. AB  A + B 2 H2O  2 H2 + O2

  22. Decomposition Reactions Harder to predict the products…always remember your diatomics. Water is often a product! HgO(s) NH4NO3 CaCO3  (Carbonates usually decompose to CO2)

  23. Decomposition Reactions HgO(s) 2HgO(s)  2Hg(l) + O2 (g) NH4NO3  NH4NO3  N2O + 2H2O CaCO3  CaO + CO2 The only way to really know is to do the reaction!!

  24. Warm Up Predict the products of the following reactions. • H2O2 • Mg + N 

  25. Warm Up Predict the products of the following reactions. • H2O2 We heat the dihydrogen dioxide and the vapor turns out to be water… 2. Mg + N  Mg3N2

  26. How are you doing on the Word Equation WS?

  27. Single Replacement • This is when one element trades places with another element in a compound. A + BC  AC + B Mg + 2H2O 

  28. Single Replacement Reactions Easy to predict the products. Look at the ions… remember that a cation has to bond to an anion!! Don’t forget about diatomics! Zn(s) + H2SO4(aq) Na(s) + H2O  OOPS! Did we balance them?

  29. Single Replacement Reactions Zn(s) + H2SO4(aq) Zn(s) + H2SO4(aq) ZnSO4(aq) + H2(g) Na(s) + H2O  Na(s) + H+OH-(l)  2Na(s)+ 2H+OH-(l)  2NaOH + H2(g)

  30. Single Replacement Reactions Reactivityof a metal makes a difference! If a metal is more reactive than the metal it is displacing a rxn will occur. If the metal is less reactive than the metal it is displacing, a rxn will not occur.

  31. Metal Reactivity Increases down a group Decreases across a period

  32. Brainiacs-- Metal Reactivity

  33. Reactivity in Single Displacement Cs + KMnO4 CsMnO4 + K Will this occur?? Na + KMnO4 NaMnO4 + K Will this occur?

  34. Double Replacement Reaction • This is when the anions and cations of two different molecules switch places, forming two entirely different compounds AB + CD AD + CB Pb(NO3)2 + 2KI PbI2 + 2KNO3

  35. Double Replacement Reactions Two ionic compounds in aqueous solution Generally 3 things happen: • A precipitate (solid) occurs Pb(NO3)2 + 2KI PbI2 + 2KNO3

  36. Double Replacement Reactions • One product is a gas that bubbles out of the mixture 2NaCN(aq) + H2SO4 2HCN(g) + Na2 SO4(aq)

  37. Double Replacement Reactions • One product is a molecule while the other products remain ions Ca(OH)2(aq) + 2HCl(aq) Ca+2 + Cl- + 2 H2O(l)

  38. Warm Up- Determine the type of reaction and predict the products. • Al + Br2  • FeO + Na  • SnCl4 • NaNO3 + CaCO3 

  39. Combustion Reactions • A combustion reaction is when oxygen combines with another compound or element producing energy. • When hydrocarbons (C?H?) combust, water, carbon dioxide and energy are produced. C10H8 + O2CO2 + H2O + Energy Can you balance it? Combustion of Naphthalene

  40. Combustion Reactions Combustion of propane: C3H8 + O2 Combustion of methane: CH4 + O2  Combustion of butene (this one is tricky!) C4H6 + O2

  41. Teacher Demo Extraordinaire!

  42. What is a flame video- Science Friday http://www.sciencefriday.com/video/06/08/2012/what-is-a-flame.html

  43. Combustion Analysis Problems…Honors Only So, we can collect the water vapor and the carbon dioxide…. do some calculations…. and determine the empirical formula of the hydrocarbon. C?H? + O2 CO2 + H2O 11.56g 2.36g

  44. Start the Types of Reactions Lab • Spend about 5 minutes on the Background. • Read through the procedure at each station. • You need to get at least 3 of the 6 stations finished today. • Goggles must be worn at all times. • Listen carefully for safety concerns while I intro the labs.

  45. Predict the products, balance and classify the following reactions. Li + MgCl2 C6H12 + O2 Ca(NO3)2 + NaOH 

  46. Warm Up- Friday Balance the following equations: C3H6 + O2 CO2 + H2O C7H14 + O2 CO2 + H2O

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