Chemistry Reviewer PDF

CHEMISTRY REVIEWER Term 2 | Lesson Cycle 1 | Reviewer by: Kirk Crisostomo (Instagram: @kkcrstmo) PHYSICAL CHANGE ​ In a physical change, matter changes form but not chemical identity. → Substance is still convertible to its original state. (Melting of ice, shredding paper, chopping w...

CHEMISTRY REVIEWER Term 2 | Lesson Cycle 1 | Reviewer by: Kirk Crisostomo (Instagram: @kkcrstmo) PHYSICAL CHANGE ​ In a physical change, matter changes form but not chemical identity. → Substance is still convertible to its original state. (Melting of ice, shredding paper, chopping wood, mixing gray and green marbles, cutting a pencil in half) ○​ There is a change in its physical properties: size, color, shape, phase. The chemical identity of the substance does not change. [Melting, Freezing, Evaporation, Condensation] CHEMICAL CHANGE ​ In a chemical change, a chemical reaction occurs and new products are formed. → Substance is NOT convertible to its original state. (Burning of wood, rotting banana, fireworks, cooking food) ○​ There is a rearrangement of atoms and formation of new substances. Properties of the new substance are significantly different from the old substance. | EVIDENCES OF CHEMICAL REACTIONS 1.​ Evolution of heat → release or absorption of energy 2.​ Evolution of gas → bubbles in a reaction 3.​ Formation of precipitate. → (Precipitate: insoluble solid formed during a reaction) 4.​ Change in color. 5.​ Change in odor. CHEMICAL EQUATION ​ A shorthand way to represent chemical reaction using symbols and formulas REACTANTS (Original Susbtance/s) ​ Substances that chemically react to produce a new substance/s PRODUCTS (Resulting Substance/s) ​ Substances that are formed from a chemical reaction. | SYMBOLS USED IN CHEMICAL EQUATION SYMBOL USE + ​ Separates reactants (combines with, reacts with) or products (and, plus) → or = ​ Separates reactants from products (yields, produces) ⇌ ​ For reversible reaction in place of a single arrow. (g) or ↑ ​ Indicates a GASEOUS reactant or product (s) or ↓ ​ Indicates a SOLID reactant or product (l) ​ Indicates a LIQUID reactant or product (aq) ​ Indicates a reactant/product in AQUEOUS solution (dissolve in water) ​ Indicates a HEAT IS SUPPLIED  ​ Indicates the use of catalyst (speeds up reaction without being consumed) | TYPES OF CHEMICAL REACTIONS 1.​ COMBUSTION ○​ Combustion reactions → a hydrocarbon reacts with oxygen gas. This is also called burning. ○​ Products are ALWAYS carbon dioxide (CO2) and water (H2O). ○​ In order to burn something, you need the 3 components in the “fire triangle.” (Fuel [hydrocarbon], Oxygen, and Something to ignite the reaction [spark]) 2.​ COMBINATION (SYNTHESIS)  ○​ The combination of 2 or more substances to form a compound. There is only ONE PRODUCT. 3.​ DECOMPOSITION ○​ A compound breaks into 2 or more simpler substances. There is only ONE REACTANT. 4.​ SINGLE DISPLACEMENT (SINGLE REPLACEMENT) ○​ Occurs when a single element (A) reacts with an ionic compound and switches places with one of the elements (B) in the compound. → An uncombined element takes the place of an element in a compound.  5.​ DOUBLE DISPLACEMENT (DOUBLE REPLACEMENT) ○​ Ions in two compounds “change partners.” Cation on one compound combines with anion of the other. WRITING A BALANCED CHEMICAL EQUATION (Balancing) | LAW OF CONSERVATION OF MASS ​ Antoine Lavoisier (1798) → “Matter cannot be created nor destroyed”. Mass of reactants = Mass of products MOLE CONCEPT AND CONVERSION ​ MOLE→ The amount of a substance of a system which contains as many elementary entities as there are atoms in 12 grams of carbon-12; its symbol is “mol” ○​ Contains 6.0221421 x 10^23 of anything. (Chemist’s dozen.) | MOLE CONCEPT AND AVOGADRO'S NUMBER ​ Lorenzo Romano Amedeo Carlo Avogadro di Queregna e di Cereto (1776-1856) ○​ Molar Mass→ The mass of a single atom of an element (in amu) is numerically equal to the mass of one mole of those atoms (in grams) ○​ One mole is a quantity of a substance that contains the same number of particles (atoms, electrons, ions, or molecules). Avogadro’s number is 6.022 x 10^23 | MOLE CONVERSION PERCENTAGE COMPOSITION ​ Shows the percentage of each constituent element in a given compound. STEPS IN FINDING THE PERCENTAGE COMPOSITION: ○​ Determine the molar mass of the compound ○​ Determine the molar mass of the element and multiply it to its subscript ○​ Enter the values in the first and second step to the given formula ○​ Round off the answer to its correct Significant Figures EXAMPLE: 1.​ Find the percent composition of C in CCl4 2.​ Find the percent composition of Cl in CCl4 EMPIRICAL AND MOLECULAR FORMULA ​ EMPIRICAL FORMULA → Represents the lowest whole number ratio of the atoms in the compound (simplest formula) THE CHEMISTRY POEM: PERCENT TO MASS → MASS TO MOLE → DIVIDE BY SMALL → MULTIPLY BY WHOLE  ​ MOLECULAR FORMULA → Shows the actual number of atoms in a compound (actual/true formula). Below are the steps in getting the Molecular formula: ○​ Get the empirical formula of the compound ○​ Determine the molar mass of the empirical formula ○​ Divide the MF Molar Mass with the EF Molar mass. Round off the quotient to the nearest small integer. ○​ Multiply the integer to all subscripts of each element to the empirical formula. EXAMPLE: 3.​ A compound that is 54.5% C, 9.1% H, and 36.4% O. Determine the empirical and molecular formula of the compound if the molecular mass is 88 g/mol.