Department of Chemistry CHEM1010 General Chemistry *********************************************** Instructor: Dr. Hong Zhang Foster Hall, Room 221 Tel:

CHEM1010/General Chemistry _________________________________________ Chapter 6. (L20)-Chemical Accounting Today’s Outline..Review of intermolecular forces..From molecules to reactions, from words to sentences: Chemical equations..Review of Lavoisier’s law: The law of mass conservation..Balance chemical reactions

Chapter 6. (L20)-Chemical Accounting Building Your Chemical Vocabulary Goethite:  -FeOOH, yellow/red stuff in soils Hematite:  -Fe 2 O 3, red stuff in soils Manganese oxide: MnO 2, black stuff in soils

Chapter 6. (L20)-Chemical Accounting Review of intermolecular forces..Major intermolecular forces Forces between polar molecules: Dipole forces (HCl, SO 2, etc.) Hydrogen bond (H 2 O, NH 3, HF, etc.) Forces between non-polar molecules Dispersion forces (H 2, O 2, Cl 2, CH 4, BF 3, etc.)

Chapter 6. (L20)-Chemical Accounting From molecules to reactions, from words to sentences: Chemical equations..Chemistry as a language Chemical letters: elements/atmos as listed in the periodic table Chemical words: compounds/molecules Chemical sentences: reactions

Chapter 6. (L20)-Chemical Accounting Chemical reactions and chemical equations..Chemistry reactions: Change of matter Iron gets rusted to become iron oxides Charcoal gets burned in the air to become carbon dioxide Hydrogen gas can burn with oxygen gas to form water..Question: Can we translate the changes of matter in everyday life language to the form in chemical language?

Chapter 6. (L20)-Chemical Accounting Chemical reactions and chemical equations..Use chemistry equations to represent chemical reactions: Chemical equations Iron gets rusted to become iron oxides: Fe + O 2  Fe 2 O 3 Charcoal gets burned in the air to become carbon dioxide C + O 2  CO 2 Hydrogen gas can burn with oxygen gas to form water H 2 + O 2  H 2 O

Chapter 6. (L20)-Chemical Accounting Balance chemical reactions..Why chemical reactions have to be balanced? Fe + O 2  Fe 2 O 3 In products 1Fe2O2Fe, 3O1Fe and 1O more C + O 2  CO 2 1C 2O 1C, 2O0C and 0O more H 2 + O 2  H 2 O 2H 2O2H, 1O 1O less

Chapter 6. (L20)-Chemical Accounting Review of Lavoisier’s law: The law of mass conservation..Lavoisier’s law: Matter is neither created nor destroyed during a chemical reaction. The total mass of the reaction products is always equal to the total mass of the reactants. In non-radioactive chemical reactions, the atoms are not destroyed, in other words, remain unchanged. What is changed is the combinations of the atoms into different molecules.

Chapter 6. (L20)-Chemical Accounting Balance chemical reactions..How to know if a chemical reaction is balanced? Lavoisier’s law requires that no atoms lost and produced in a chemical reaction. Rule for balancing a chemical reaction: Do an accounting for each atom involved in the chemical reaction (atom accounting) Make sure the number of atoms for each atom in the reactant side is the same for each atom in the product side, no more, and no less In other words, the atoms are balanced

Chapter 6. (L20)-Chemical Accounting Balance chemical reactions..How to balance chemical reactions? Fe + O 2  Fe 2 O 3 4Fe + 3O 2 = 2Fe 2 O 3 4Fe 6O 4Fe, 6O C + O 2  CO 2 C + O 2 = CO 2 H 2 + O 2  H 2 O 2H 2 + O 2 = 2H 2 O 4H 2O 4H, 2O

Chapter 6. (L20)-Chemical Accounting Balance chemical reactions..How to balance chemical reactions? Tip: Balance the atom with odd number first NaN 3  N 2 + Na 2NaN 3 = 3N 2 + 2Na 2Na, 6N 6N 2Na

Chapter 6. (L20)-Chemical Accounting Balance chemical reactions..How to balance chemical reactions? Tip: Balance the atom with odd number first N 2 + H 2  NH 3 N 2 + 3H 2 = 2NH 3 2N 6H 2N, 6H

Chapter 6. (L20)-Chemical Accounting Balance chemical reactions..How to balance chemical reactions? CH 4 + O 2  CO 2 + H 2 O CH 4 + 2O 2 = CO 2 + 2H 2 O 1C, 4H, 4O 1C, 4O, 4H

Chapter 6. (L20)-Chemical Accounting Balance chemical reactions..How to balance chemical reactions? C 4 H 10 + O 2  CO 2 + H 2 O 2C 4 H O 2 = 8CO H 2 O 8C, 20H, 26O 8C, 26O, 20H

Chapter 6. (L20)-Chemical Accounting Balance chemical reactions..How to balance chemical reactions? C 3 H 8 + O 2  CO 2 + H 2 O C 3 H 8 + 5O 2 = 3CO 2 + 4H 2 O 3C, 8H, 10O 3C, 10O, 8H

Chapter 6. (L20)-Chemical Accounting Quiz Time The balance of any (non-radioactive) chemical reactions is required by (a) Dalton’s atomic theory; (b) Bohr’s atomic theory; (c) Lavoisier’s law of mass conservation; (d) the quantum mechanic model of atoms.

Chapter 6. (L20)-Chemical Accounting Quiz Time How many Ca, P, and O atoms are in 2Ca 3 (PO 4 ) 2, respectively? (a) 3, 1, 4; (b) 3, 2, 8; (c) 6, 4, 16; (d) 6, 2, 4.

Chapter 6. (L20)-Chemical Accounting Quiz Time How many N, H, and O atoms are in 2NH 4 NO 3, respectively? (a) 2, 4, 3; (b) 2, 8, 3; (c) 4, 8, 6; (d) 2, 4, 6.

Chapter 6. (L20)-Chemical Accounting Quiz Time How many C, H, and O atoms are in 2C 6 H 5 COOH, respectively? (a) 7, 6, 2; (b) 14, 12, 4; (c) 12, 10, 2; (d) 6, 5, 2.

Chapter 6. (L20)-Chemical Accounting Quiz Time Which of the following reactions is balanced ? (a) H 2 + Cl 2 = HCl; (b) H 2 + 2Cl 2 = HCl; (c) H 2 + Cl 2 = 2HCl; (d) 2H 2 + Cl 2 = HCl.

Chapter 6. (L20)-Chemical Accounting Quiz Time Which of the following reactions is balanced ? (a) 2NH 3 + O 2 = N 2 + H 2 O; (b) NH 3 + O 2 = N 2 + 2H 2 O; (c) 2NH 3 + 2O 2 = N 2 + 3H 2 O; (d) 4NH 3 + 3O 2 = 2N 2 + 6H 2 O.

Chapter 6. (L20)-Chemical Accounting Quiz Time Which of the following reactions is balanced ? (a) K + H 2 O = KOH + H 2 ; (b) Mg + H 2 O = Mg(OH) 2 + H 2 ; (c) 4Fe + 3O 2 = 2Fe 2 O 3 ; (d) N 2 + O 2 = NO 2.

Chapter 6. (L20)-Chemical Accounting Quiz Time Which of the following reactions is balanced ? (a) C 2 H 4 + O 2 = 2CO 2 + 2H 2 O; (b) Mg(OH) 2 + 2HCl = MgCl 2 + H 2 O; (c) Fe 2 O 3 ; + 6HCl = 2FeCl 3 + 3H 2 O; (d) N 2 + O 2 = NO.

Chapter 6. (L20)-Chemical Accounting Quiz Time Which of the following is appropriate for balancing the reaction: C 2 H 4 + O 2 = CO 2 + H 2 O? (a) H 2 O; (b) 3CO 2 ; (c) 3O 2 ; (d) 2C 2 H 4.

Chapter 6. (L20)-Chemical Accounting Quiz Time Which of the following is appropriate for balancing the reaction: C 4 H 10 + O 2 = CO 2 + H 2 O? (a) 5H 2 O; (b) 4CO 2 ; (c) 13O 2 ; (d) C 2 H 10.