SAGS Definitions - Chemistry

Question 1

What is the purpose of balanced chemical equations?

Answer 1

Balanced chemical equations represent chemical changes, translating word equations into chemical equations with formulae.

Question 2

How do you interpret the meaning of state symbols (s), (ℓ), (g), and (aq) in a chemical equation?

Answer 2

State symbols represent phases, and they indicate whether a substance is in a solid, liquid, gas, or aqueous state.

Question 3

How can you balance reaction equations by inspection?

Answer 3

Balancing reaction equations involves adjusting coefficients to ensure that the number of atoms of each element is the same on both sides of the equation.

Question 4

Provide the names and formulas of the polyatomic ions ammonium, chlorate, ethanoate, hydroxide, nitrate, nitrite, permanganate, carbonate, hydrogen carbonate, sulfate, hydrogen sulfate, thiosulfate, sulfite, phosphate, and dichromate.

Answer 4

Ammonium (NH₄⁺), chlorate (ClO₃⁻), ethanoate (C₂H₃O₂⁻), hydroxide (OH⁻), nitrate (NO₃⁻), nitrite (NO₂⁻), permanganate (MnO₄⁻), carbonate (CO₃²⁻), hydrogen carbonate (HCO₃⁻), sulfate (SO₄²⁻), hydrogen sulfate (HSO₄⁻), thiosulfate (S₂O₃²⁻), sulfite (SO₃²⁻), phosphate (PO₄³⁻), and dichromate (Cr₂O₇²⁻).

Question 5

How do you write the chemical formula of a compound when given its name, including the use of Stock notation?

Answer 5

Use the periodic table and knowledge of polyatomic ions to write chemical formulae when given the name of a chemical compound, possibly including Stock notation.

Question 6

What does the mole represent as the SI unit for the amount of substance?

Answer 6

The mole represents the amount of substance in a chemical system.

Question 7

How is the mole related to the relative atomic mass?

Answer 7

The mole is related to the relative atomic mass, and one mole contains Avogadro’s number of particles (NA = 6.02 × 10²³ mol⁻¹).

Question 8

Define molar mass and provide the formula for calculating it.

Answer 8

Molar mass is the mass in grams of one mole of a substance. The formula for calculating it is M = m/n, where M is molar mass, m is mass, and n is the number of moles.

Question 9

How do you calculate the number of moles using the equation n = m/M?

Answer 9

To calculate the number of moles (n), use the equation n = m/M, where m is the mass of the substance, and M is the molar mass.

Question 10

What is the molar volume of a gas at Standard Temperature and Pressure (STP)?

Answer 10

The molar volume of a gas at STP is 22.4 dm³/mol.

Question 11

When does STP occur, and what are the conditions (temperature and pressure)?

Answer 11

STP occurs at 0 °C (273 K) and at 1 atmosphere (101.3 kPa).

Question 12

How do you solve problems involving the molar volume of gases using the equation n = V/Vm?

Answer 12

Solve problems by using the equation n = V/Vm, where Vm is the molar volume at STP (22.4 dm³/mol).

Question 13

What is a solution, and how is it defined?

Answer 13

A solution is a homogeneous mixture of solute and solvent.

Question 14

Define solute and provide an example.

Answer 14

Solute is the substance that is dissolved in a solution. For example, in saltwater, salt is the solute.

Question 15

Define solvent and give an example.

Answer 15

Solvent is the substance in which another substance is dissolved to form a solution. In a sugar-water solution, water is the solvent.

Question 16

What is the definition of concentration in the context of solutions?

Answer 16

Concentration is the amount of solute per unit volume of solution.

Question 17

How do you calculate the molar concentration of a solution using the equation c= n/V or c= m/MV

Answer 17

The molar concentration (c) of a solution can be calculated using the equation c= n/V or c= m/MV where c is concentration, V is volume, M is molarity, and n is the number of moles of solute.

Question 18

What does yield measure in the context of a chemical reaction?

Answer 18

Define yield as a measure of the extent of a reaction, generally measured by comparing the amount of product against the amount of product that is possible. It is often expressed as a percentage.

Question 19

How do you perform stoichiometric calculations involving the percentage yield of a chemical reaction?

Answer 19

To calculate the percentage yield, divide the actual yield by the theoretical yield and multiply by 100.

Question 20

Define stoichiometric calculations and provide an example involving moles.

Answer 20

Stoichiometric calculations involve using balanced equations to relate quantities of reactants and products. For example, if given the number of moles of one substance, the balanced equation can be used to find the moles of another substance involved in the reaction.

Question 21

Define percentage purity and explain how to perform stoichiometric calculations involving it.

Answer 21

Percentage purity measures the proportion of a substance that is the desired compound. To perform stoichiometric calculations involving percentage purity, use the percentage to determine the actual amount of the pure substance.

Question 22

What is an intramolecular bond, and where does it occur?

Answer 22

An intramolecular bond occurs between atoms within molecules.

Question 23

Define a covalent bond and differentiate between non-polar covalent and polar covalent bonds.

Answer 23

A covalent bond involves the sharing of at least one pair of electrons between two non-metal atoms. Non-polar covalent bonds have equal sharing of electrons, while polar covalent bonds result from unequal sharing, creating a dipole due to electronegativity differences.

Question 24

What is electronegativity, and how is it used to determine the type of covalent bond?

Answer 24

Electronegativity is a measure of an atom’s tendency to attract a bonding pair of electrons. Using electronegativity numbers, a zero difference indicates a non-polar covalent bond, a non-zero difference indicates a polar covalent bond, and the greater the difference, the more polar the bond.

Question 25

How is an ionic bond defined?

Answer 25

An ionic bond is defined as the transfer of electrons between atoms, followed by electrostatic attraction between oppositely charged ions.

Question 26

Between which types of elements does ionic bonding generally occur?

Answer 26

Ionic bonding generally occurs between metals (or ammonium ions) and non-metals (or polyatomic ions).

Question 27

Define metallic bonding and describe its components.

Answer 27

Metallic bonding occurs between a positive kernel (metal cations) and a sea of delocalized electrons.

Question 28

What is the definition of intermolecular force?

Answer 28

Intermolecular force is a force of attraction between molecules, ions, or atoms of noble gases.

Question 29

Differentiate between intermolecular forces and intramolecular bonds.

Answer 29

Intermolecular forces occur between molecules, ions, or atoms, while intramolecular bonds occur within molecules.

Question 30

State whether van der Waals forces are intermolecular or intramolecular.

Answer 30

Van der Waals forces are intermolecular forces.

Question 31

Name and explain the origin of three types of van der Waals forces.

Answer 31

Dipole-dipole forces/interactions arise from the attraction between the positive end of one polar molecule and the negative end of another.

London forces (induced dipole or dispersion forces) result from temporary fluctuations in electron distribution.

Hydrogen bonding, a special case of dipole-dipole forces, occurs when hydrogen is bonded to a small atom of high electronegativity with at least one lone pair of electrons.

Question 32

Where do hydrogen bonds exist, and what are the conditions for their formation?

Answer 32

Hydrogen bonds exist between polar molecules where hydrogen is bonded to a small atom of high electronegativity with at least one lone pair of electrons.

Question 33

Explain the involvement of London forces in all interactions between particles.

Answer 33

All interactions between particles involve some form of London forces.

Question 34

How is the strength of London forces influenced, and what factors affect it?

Answer 34

The strength of London forces is influenced by the size of temporary dipoles, which, in turn, is affected by the number of electrons and the interacting surface of the molecule.

Question 35

What is the predominant (strongest) intermolecular force in a substance?

Answer 35

The predominant (strongest) intermolecular force in a substance determines its overall behavior and properties.

Question 36

Why do giant structures like diamond, graphite, and silicon dioxide have high melting and boiling points?

Answer 36

The high melting and boiling points in giant structures are attributed to the large amount of energy needed to break numerous strong covalent bonds within the structure.

Question 37

What determines the melting and boiling points of giant ionic solids, such as sodium chloride?

Answer 37

The melting and boiling points of giant ionic solids are determined by the electrostatic forces of attraction (ionic bonds) between the cations and anions in the lattice structure.

Question 38

How do the melting and boiling points of simple molecular substances relate to intermolecular forces?

Answer 38

For simple molecular substances, the melting and boiling points are influenced by the strength and relative number (for hydrogen bonds) of intermolecular forces.

Question 39

When comparing melting and boiling points within the same group or homologous series, what primarily accounts for the differences, especially in substances like halogens or hydrides?

Answer 39

The differences in melting and boiling points are mainly due to London forces, except for substances that experience hydrogen bonds (e.g., H2S vs. H2O).

Question 40

What factors contribute to differences in melting and boiling points between substances of similar mass in different groups or homologous series?

Answer 40

The differences are due to the presence of other intermolecular forces (dipole-dipole and/or hydrogen bonds) in addition to the London forces, which are present between all particles.

Question 41

In substances involving hydrogen bonding, what primarily influences the differences in melting and boiling points?

Answer 41

The relative number of hydrogen bonds between particles primarily influences the differences in melting and boiling points (e.g., HF vs. H2O or propanol vs. ethanediol).

Question 42

Why do metals and graphite conduct electricity?

Answer 42

Metals and graphite conduct electricity due to the presence of free (mobile) valence electrons.

Question 43

When do ionic compounds conduct electricity, and why?

Answer 43

Ionic compounds conduct electricity only when molten or in aqueous solution because of the presence of free (mobile) ions, which are not present in the solid state.

Question 44

What is the definition of heat of reaction (ΔH)?

Answer 44

ΔH is defined as the net change of chemical potential energy of the system.

Question 45

How are exothermic reactions characterized?

Answer 45

Exothermic reactions transform chemical potential energy into thermal energy.

Question 46

Define endothermic reactions.

Answer 46

Endothermic reactions transform thermal energy into chemical potential energy.

Question 47

What is the relationship between bond breaking, bond formation, and energy changes?

Answer 47

Bond breaking is endothermic, while bond formation is exothermic.

Question 48

Predict the sign of ΔH for endothermic and exothermic reactions.

Answer 48

ΔH > 0 for endothermic reactions and ΔH < 0 for exothermic reactions.

Question 49

What happens to the temperature in exothermic and endothermic reactions?

Answer 49

Exothermic reactions release heat, increasing the temperature, while endothermic reactions absorb heat, decreasing the temperature.

Question 50

Define activation energy.

Answer 50

Activation energy is the minimum energy required to start a chemical reaction or the energy needed to form the activated complex.

Question 51

Explain the activated complex.

Answer 51

The activated complex is a high-energy, unstable, temporary transition state between reactants and products.

Question 52

What is the role of a catalyst in a reaction?

Answer 52

A catalyst increases the rate of the reaction but remains unchanged at the end.

Question 53

How does collision theory explain reaction rate?

Answer 53

Collision theory states that a reaction proceeds only when reactant particles collide effectively, with the correct orientation and sufficient energy.

Question 54

Define reaction rate.

Answer 54

Reaction rate is the change in concentration per unit time of either a reactant or product.

Question 55

What factors affect the rate of chemical reactions?

Answer 55

Factors include the nature of reacting substances, surface area of a solid, concentration of a solution, pressure of a gas, temperature, and the presence of a catalyst.

Question 56

Explain the collision theory’s role in reaction rates.

Answer 56

Reaction rate is directly proportional to the number of effective collisions per unit time, according to the collision theory.

Question 57

How do you distinguish between average and instantaneous reaction rates?

Answer 57

Average reaction rates involve changes over time, while instantaneous rates focus on a specific moment.

Question 58

Define a closed system in chemistry.

Answer 58

A closed system conserves mass but allows energy to enter or leave freely.

Question 59

What is Le Châtelier’s principle?

Answer 59

Le Châtelier’s principle states that when an external stress is applied to a system in dynamic chemical equilibrium, the equilibrium point changes to counteract the stress.

Question 60

How does a catalyst affect a system in equilibrium?

Answer 60

A catalyst speeds up both the forward and reverse reactions equally, having no effect on the position of equilibrium.

Question 61

Write an expression for the equilibrium constant (Kc).

Answer 61

Kc expression is written from the given reaction equation, involving concentrations.

Question 62

What influences the value of the equilibrium constant (Kc)?

Answer 62

Temperature is the only factor influencing the value of Kc.

Question 63

Use Le Châtelier’s principle to predict the effects of changes on equilibrium concentrations.

Answer 63

Changes in pressure, temperature, and concentration affect equilibrium concentrations as the system adjusts to counteract the stress.