chemistry

Question 1

Define the periodic table.

Answer 1

Arrangement of elements by increasing atomic number, showing periodic trends.

Question 2

Explain groups and periods on the periodic table.

Answer 2

Groups: vertical columns with similar properties; Periods: horizontal rows showing gradual changes in properties.

Question 3

Define electronegativity.

Answer 3

Measure of an atom’s ability to attract electrons in a bond.

Question 4

Explain ionization energy.

Answer 4

Energy required to remove an electron from an atom in the gaseous state.

Question 5

Describe atomic radius and its trend.

Answer 5

Atomic radius is the size of an atom, which decreases across a period and increases down a group.

Question 6

Define electron affinity.

Answer 6

Energy change when an atom gains an electron.

Question 7

Describe metallic and nonmetallic character.

Answer 7

Metallic character increases down a group and decreases across a period; nonmetallic character shows the opposite trend.

Question 8

Explain the properties of alkali metals.

Answer 8

Highly reactive, soft metals with one valence electron, found in Group 1.

Question 9

Describe the halogens and their properties.

Answer 9

Reactive nonmetals in Group 17, with seven valence electrons, forming salts with metals.

Question 10

Define noble gases and their characteristics.

Answer 10

Elements in Group 18; inert gases with full valence shells, very low reactivity.

Question 11

Define chemical reaction.

Answer 11

Process where reactants convert into products with new chemical properties.

Question 12

Describe the law of conservation of mass.

Answer 12

Mass is conserved in a chemical reaction; total mass of reactants equals total mass of products.

Question 13

Define a mole and Avogadro’s number.

Answer 13

Mole: amount of substance containing 6.022 × 10^23 particles (Avogadro’s number).

Question 14

Explain molar mass and how to calculate it.

Answer 14

Molar mass is the mass of one mole of a substance, calculated by summing atomic masses.

Question 15

Define empirical and molecular formulas.

Answer 15

Empirical formula: simplest ratio of elements; Molecular formula: actual number of atoms in a molecule.

Question 16

Explain the process of balancing chemical equations.

Answer 16

Ensure the same number of each atom on both sides of the equation.

Question 17

Define limiting reactant.

Answer 17

The reactant that is completely used up, limiting the amount of product formed.

Question 18

Explain percent yield and its formula.

Answer 18

Percent yield = (actual yield / theoretical yield) × 100.

Question 19

Define exothermic and endothermic reactions.

Answer 19

Exothermic: releases energy; Endothermic: absorbs energy.

Question 20

Describe activation energy.

Answer 20

Minimum energy required to initiate a chemical reaction.

Question 21

Define acid and base according to Arrhenius.

Answer 21

Acid: produces H⁺ ions in water; Base: produces OH⁻ ions in water.

Question 22

Define acid and base according to Bronsted-Lowry.

Answer 22

Acid: proton donor; Base: proton acceptor.

Question 23

Describe the pH scale.

Answer 23

Scale from 0 to 14 measuring acidity/alkalinity; 7 is neutral, below 7 is acidic, above 7 is basic.

Question 24

Explain the pH formula and how to calculate it.

Answer 24

pH = -log[H⁺], where [H⁺] is the concentration of hydrogen ions.

Question 25

Define strong and weak acids.

Answer 25

Strong acids completely ionize in water; Weak acids partially ionize.

Question 26

Explain neutralization reaction.

Answer 26

Reaction between an acid and a base, producing water and a salt.

Question 27

Define buffer solution.

Answer 27

Solution that resists changes in pH when small amounts of acid/base are added.

Question 28

Explain the role of conjugate acid-base pairs.

Answer 28

Conjugate pairs differ by one proton; acid donates a proton, base accepts it.

Question 29

Describe titration and its purpose.

Answer 29

Technique to determine concentration of a solution using a known reactant.

Question 30

Define the equivalence point in titration.

Answer 30

Point where moles of acid equal moles of base in a titration.

Question 31

Define enthalpy (H).

Answer 31

Heat content of a system at constant pressure.

Question 32

Explain Hess’s Law.

Answer 32

The enthalpy change of a reaction is the same, regardless of the reaction pathway.

Question 33

Define standard enthalpy change of formation.

Answer 33

Enthalpy change when 1 mole of a compound is formed from its elements in standard states.

Question 34

Describe endothermic and exothermic reactions in terms of enthalpy.

Answer 34

Endothermic: positive enthalpy change; Exothermic: negative enthalpy change.

Question 35

Explain activation energy in kinetics.

Answer 35

Minimum energy required for a reaction to occur.

Question 36

Define catalyst and its effect on reaction rate.

Answer 36

Catalyst speeds up a reaction without being consumed, by lowering activation energy.

Question 37

Describe the collision theory of reactions.

Answer 37

For a reaction to occur, particles must collide with sufficient energy and proper orientation.

Question 38

Explain rate of reaction and how it’s measured.

Answer 38

Change in concentration of reactants/products per unit time; measured by change in mass, volume, or color.

Question 39

Define reaction mechanism.

Answer 39

Series of steps that show the pathway from reactants to products.

Question 40

Explain Le Chatelier’s Principle.

Answer 40

If a dynamic equilibrium is disturbed, the system shifts to counteract the disturbance.

Question 41

Define organic chemistry.

Answer 41

Study of carbon-containing compounds and their reactions.

Question 42

Describe alkanes and give an example.

Answer 42

Saturated hydrocarbons with single bonds; Example: methane (CH₄).

Question 43

Define alkenes and their general formula.

Answer 43

Unsaturated hydrocarbons with double bonds; Formula: CₙH₂ₙ.

Question 44

Describe alkynes and their general formula.

Answer 44

Unsaturated hydrocarbons with triple bonds; Formula: CₙH₂ₙ₋₂.

Question 45

Define functional group and give examples.

Answer 45

Specific groups of atoms that determine properties of organic molecules; Examples: -OH, -COOH.

Question 46

Describe alcohols and their general formula.

Answer 46

Organic compounds with -OH group; General formula: CₙH₂ₙ₊₁OH.

Question 47

Define carboxylic acids and their properties.

Answer 47

Organic acids with -COOH group; weakly acidic with sour taste.

Question 48

Describe esters and their formation.

Answer 48

Formed by reaction between acids and alcohols, used in fragrances and flavors.

Question 49

Explain isomers and types of isomerism.

Answer 49

Compounds with the same molecular formula but different structures; Types: structural and stereoisomerism.

Question 50

Describe polymers and give examples.

Answer 50

Large molecules made of repeating units; Examples: polyethylene, proteins.

Question 51

Define chemical equilibrium.

Answer 51

State where forward and reverse reaction rates are equal, and concentrations remain constant.

Question 52

Describe equilibrium constant (Kc).

Answer 52

Ratio of product to reactant concentrations at equilibrium, specific to a reaction at a given temperature.

Question 53

Explain the effect of temperature on equilibrium.

Answer 53

Increasing temperature favors endothermic reactions, while decreasing temperature favors exothermic reactions.

Question 54

Define redox reaction.

Answer 54

Reaction involving transfer of electrons, with oxidation and reduction occurring simultaneously.

Question 55

Explain oxidation and reduction.

Answer 55

Oxidation: loss of electrons; Reduction: gain of electrons.

Question 56

Describe the role of an oxidizing agent.

Answer 56

Substance that gains electrons and is reduced in a redox reaction.

Question 57

Define electrochemical cell and its components.

Answer 57

Device generating electricity from a redox reaction, with electrodes and electrolyte.

Question 58

Explain standard electrode potential (E°).

Answer 58

Measure of the tendency of a half-cell to gain or lose electrons under standard conditions.

Question 59

Describe the function of a salt bridge in a galvanic cell.

Answer 59

Maintains electrical neutrality by allowing ion flow between half-cells.

Question 60

Explain Faraday’s laws of electrolysis.

Answer 60

First law: mass of substance deposited is proportional to charge; Second law: mass deposited is proportional to molar mass.