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Chemical Reactions and Balancing Equations in Chemistry

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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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