University:
University of North Carolina at Charlotte
Course:
CHEM 1251 | General Chemistry I
Academic year:

2024
Views:

76

Pages:

5
Author:

Kamila P.

Chapter 8: Chemical Reactions Chemical Change vs Physical Change "Changes that alter the composition of matter are chemical changes." "Changes that alter only the state or appearance, but not composition, are physical changes." Writing and Balancing Chemical Reactions "Reactions involve chemical changes in matter resulting in new substances." "Reactions involve rearrangement and exchange of atoms to produce new molecules." Reactants → Products "A chemical reaction is a written statement of: the relative quantities, the chemical identity (formulas) of the substances in the reaction, and their physical state." Example: CH₄(g) + 2O₂(g) → CO₂(g) + 2H₂O(l) (s) = solid (aq) = aqueous (dissolved in water) QUANTITIES IN CHEMICAL REACTIONS "The amount of every substance used or made in a chemical reaction is related to the amounts of all the other substances in the reaction." Law of conservation of mass: Balancing equations by balancing atoms. STOICHIOMETRY: The numerical relationship between the quantities of reactants and products in a chemical reaction. WRITING AND BALANCING CHEMICAL EQUATIONS Write a balanced equation for the reaction between solid cobalt(III) oxide and solid carbon that produces solid cobalt and carbon dioxide gas. Write skeletal (unbalanced) equation: (chemical formulas) Balance atoms that occur in more complex substances first: (always balance atoms in compounds before elements) Balance free element atoms last: (balance free elements by adjusting the coefficient on the free element) If equation has fractions, clear by multiplying Check by summing the total number of each type of atom on both sides of the equation. Balancing Chemical Equations Example 1: Unbalanced equation: Co₂O₃(s) + C(s) → Co(s) + CO₂(s) Balanced equation: 2Co₂O₃(s) + 3C(s) → 4Co(s) + 3CO₂(g) Combustion of Ethane: Unbalanced equation: C₂H₆(g) + O₂(g) → CO₂(g) + H₂O(g) Balanced equation: 2C₂H₆(g) + 7O₂(g) → 4CO₂(g) + 6H₂O(g) Another Reaction: 3CaCl₂(aq) + 2Na₃PO₄(aq) → Ca₃(PO₄)₂(s) + 6NaCl(aq) Diatomic Elements: Br₂, I₂, N₂, Cl₂, H₂, O₂, F₂