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Chemical Reactions and Balancing Equations in Chemistry

Learn about chemical reactions, balancing equations, conservation of mass, moles, molar mass, and types of reactions. Practice balancing equations and calculating molar mass with examples and activities.

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Chemical Reactions and Balancing Equations in Chemistry

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  1. Chapter 7 Chemical Reactions

  2. 7-1 Describing Reactions • In a chemical __________, the substances that undergo change are called ___________ • The new substances formed as a result of that change are called ___________ • _________  ____________ • Ex. Carbon + oxygen  carbon dioxide • ________ equation

  3. Chemical equations • Ex. C + O2 CO2 • Chemical _________ • A chemical __________ is a representation of a chemical reaction in which the reactants and products are expressed as ____________

  4. Conservation of Mass • During chemical reactions, the________ of the products is always_______ to the mass of the reactants. • Established by Antoine Lavoisier and is known as the_____________________ • The law of conservation of mass states that mass is neither _________ nor __________ in a chemical reaction

  5. How is mass conserved in chemical change? Activity • Follow the directions on page 191 in your book • Fill out following information • Mass of the bag and the water=____________ • Mass of a square piece of paper with sides 10cm__________________ • Mass of the tablet and the paper together____________ • Mass of just the tablet_______________ • The combined masses of the bag, the water, and the tablet___________ • Mass of the bag and its contents_____________

  6. Activity questions • How do you know whether a chemical change took place?

  7. Activity Question • What happened to the mass of the plastic bag and its contents after the bubbling stopped? • What might this information tell you about a chemical change?

  8. Balancing Equations7-1 Continued • In order to show that mass is conserved during a reaction, a chemical equation must be _________ • You can balance a chemical equation by changing the_________, the numbers that appear _________ the formulas • As you balance equations, you should never change the ___________ in a formula

  9. Steps to balancing equations • Count the _________ of atoms of each element on each side of the equation • Ex: N2H4 + O2 N2 + H2O • Left side has ____ nitrogen,____hydrogen, and ______ oxygen atoms • The right side has ____nitrogen,_____hydrogen, and____oxygen atom • The hydrogen and oxygen atoms need to be_______.

  10. Steps to balancing equations 6. Change one or more coefficients until the equation is balanced _1_N2H4 + _1_O2 _1_N2 + _2_H2O • The equation is now balanced • Each side has _____ nitrogen,_____ oxygen, and _______ hydrogen atoms

  11. Practice Balancing equations problems • ___Na + ___H2O ____NaOH + ___H2 • ___HCl + ___CaCO3  ____CaCl2 +___CO2 + ____H2O • ____Al + ____Cl2  _____AlCl3 • ___Cu + _____O2  _____CuO • ____H2O2  ____H2O + ____O2

  12. What is a MOLE? It is a number of things….. - Just like a dozen 1 dozen eggs = 12 eggs So, instead of 12 the mole is equal to 602 billion trillion – OR- 6.02 x 1023 602 000 000 000 000 000 000 000

  13. Just How Big is a Mole? 6.02 X1023  Pennies: Would make at least 7 stacks that would reach the moon.

  14. How Big is a mole? Cover the earth to a depth of 200 miles with soft drink cans. Cover the USA to a depth of 9 miles of unpopped popcorn kernels.

  15. The mole is many things…. 1 dozen cookies = 12 cookies 1 mole of cookies = 6.02 x 1023 cookies 1 dozen cars = 12 cars 1 mole of cars = 6.02 x 1023 cars 1 dozen Al atoms = 12 Al atoms 1 mole of Al atoms = 6.02 x 1023 atoms NOTE: the mole is abbreviated mol (gee, that’s a lot quicker to write……)

  16. Molar Mass • Mass of 1 ______ of a pure substance • Numerically equal to the atomic mass but expressed in _______ • The atomic mass of carbon is 12.0____, so the molar mass of carbon is 12.0_____

  17. What is the molar mass of the following: • Potassium ? Nickel ?

  18. What is the atomic mass of the following: • Potassium ? Nickel ?

  19. Practice • What is the molar mass of the following: • KCl • C2H6 • CaCO3 • H2O

  20. Homework/More Practice • What is the molar mass of the following: • HCl • NaCl • CaO

  21. Homework/More Practice • Balance the following ___Na + ____H2O ___H2 + ___NaOH ___C2H6 + ____O2  ___CO2 + ___H2O

  22. Beaker Breaker • Calculate the molar mass of the following: • MgCl2 • CaBr2

  23. Gram- Mole Conversions

  24. How many grams are needed to have 0.852 moles gold? • 0.852 mol Au g Au 1 mol Au = ______g Au

  25. Convert 2.50moles of KClO3 to grams

  26. Calculate how many grams are in 0.700moles of H2O2?

  27. How many moles are in 55 g of lead? • g Pb mol Pb 1 g Pb • = _______moles Pb

  28. How many moles are in 86.1 g sodium? • 86.1 g ? mole Na = 1 ? g • 86.1 g mole Na = 1 g • _______moles Na

  29. How many moles are in 22 grams of copper metal?

  30. 7-2 Types of Reactions • General types of chemical reactions • ______________ • ______________ • ______________ • ______________ • ______________

  31. Single Replacement • ________________ reaction is a reaction in which one element takes place of another element in a compound. • A + BC  B + AC

  32. Teacher Demonstration • See handout • Cu + 2AgNO32Ag + Cu(NO3)2 • Copper replaces the silver nitrate to form copper(II) nitrate • The products is_______, which you can see. The other product is_____________, gives the solution its blue color.

  33. 7-2 Continued Reactions as Electron Transfer • The discovery of subatomic particles enabled scientists to classify certain chemical reactions as transfers of_______________ between atoms. • A reaction in which electrons are transferred from one reactant to another is called an ____________________ reaction, _________ reaction

  34. Oxidation • Synthesis reactions, in which a____________combines with__________, traditionally have been classified as oxidations. • 2Ca +O2  2_________ • Ca  Ca+2 + 2e- • Calcium ________ two electrons • A reactant is_________ if it loses electrons

  35. Reduction • As calcium atoms lose electrons during the synthesis of calcium oxide, the oxygen________ electrons • O + 2e-  O2- • The process in which an element gains electrons during a chemical reaction is called____________ • A reactant is said to be______________ if it gains electrons. • Oxidation and reduction always occur________.

  36. Beaker Breaker • Identify the following reactions as either synthesis, decomposition, single replacement, double replacement, or combustion: 2C2H6 + 7O2 4CO2 + 6H2O Ca + 2HCl  CaCl2 + H2

  37. Beaker Breaker Cont. • Write a paragraph explaining why the formation of water can be classified as a synthesis or combustion.

  38. 7-3 Energy Changes in ReactionsChemical Bonds and Energy • Heat produced by a_________(C3H8) grill is a form of energy • Balance equation: • C3H8 + ____O2___CO2 +___H2O • _________ will be added to the right side of the equation

  39. Propane Combustionusing models • C3H8 + 5O2 3CO2 + 4H2O • Open to page 207 follow Figure 17

  40. Chemical Energy • _____________ is the energy stored in the chemical bonds of a substance. • Using the models to make C3H8 (propane) • How many C-H bonds_________ • How many C-C bonds_________

  41. Chemical Bonds • Chemical _________ involve the________ of chemical bonds in the __________ and the_______ of chemical bonds in the ________. • Each propane molecule reacts with_______ oxygen molecules. • In order for the reaction to occur, the ____ C-H single bonds, _____ C-C single bonds and____O=O double bonds must be broken. • Breaking bonds require energy • Propane grills require a igniter to provide enough energy to ________the bonds

  42. Chemical Bonds • After the reaction of propane (it is burned) occurs, ______molecules of carbon dioxide (CO2)and ______ molecules of water (H2O) are formed. • There is _____ C=O double bonds and ____ O-H single bonds formed as the ________. • Forming bonds__________ energy • ________and ________ given off by a propane stove are the results from the formation of the new chemical bonds

  43. Homework • Section 7-2 Review • #1 , 3, 4, 5

  44. Beaker Breaker • Identify the following reactions as either single displacement, double displacement, decomposition, synthesis, or combustion • NaCl + H2SO4  K2SO4 + H2O • CaO + CO2  CaCO3 • MgCl2  Mg + Cl2

  45. 7-3 ContinuedExothermic and Endothermic Reactions • During a chemical reaction, energy is either ________ or ___________ • A chemical reaction that_________ energy to its surroundings is called an_____________ reaction • Ex: Freezing • A chemical reaction that__________ energy from its surroundings is called an____________ • Ex: Melting

  46. Exothermic Reactions • In exothermic reactions, the energy released as the products form is __________ than the energy required to break the bonds in the reactants • Example – Combustion • C3H8 + 5O2 3CO2 + 4H2O + 2220kJ

  47. Endothermic Reactions • In an endothermic reaction, more energy is required to___________ the bonds in the reactants than is released by the formation of the products. • Example: The decomposition of mercury (II) oxide • 2HgO + 181.7kJ  2Hg + O2

  48. Conservation of Energy • The law of____________________ states in exothermic and endothermic reactions the total amount of energy before and after the reaction is the same.

  49. Homework • 7-3 Section Review page 209 • Numbers 1,2,3

  50. Ticket Out the Door • Please explain in a few sentences how melting is an example of an endothermic reaction

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