UNIT 1

Question 1

What observable changes occur during chemical reactions, and what do these changes indicate about energy?

Answer 1

During chemical reactions, observable changes include temperature fluctuations and light emission. These changes indicate energy transfers, where exothermic reactions release heat (temperature increase) and endothermic reactions absorb heat (temperature decrease)

Question 2

What is the difference between exothermic and endothermic reactions in terms of heat energy and enthalpy change (ΔH)?

Answer 2

Exothermic Reactions: Release heat energy, resulting in a negative enthalpy change (ΔH < 0). Example: Combustion of methane.
Endothermic Reactions: Absorb heat energy, resulting in a positive enthalpy change (ΔH > 0). Example: Photosynthesis

Question 3

How is heat energy related to temperature, and what does temperature measure in terms of particle energy?

Answer 3

Heat is a form of energy transferred between systems or surroundings. Temperature measures the average kinetic energy of the particles in a substance. Higher temperatures indicate higher average kinetic energy

Question 4

How can you determine if a thermochemical reaction is exothermic or endothermic from enthalpy level diagrams and equations?

Answer 4

Enthalpy Level Diagrams: An exothermic reaction shows products at a lower energy level than reactants, while an endothermic reaction shows products at a higher energy level.
Thermochemical Equations: Exothermic reactions have a negative ΔH, while endothermic reactions have a positive ΔH.

Question 5

Why are some reactions exothermic and others endothermic based on bond enthalpies?

Answer 5

Reactions are exothermic if the energy released from forming bonds is greater than the energy required to break bonds. They are endothermic if more energy is required to break bonds than is released when new bonds form

Question 6

How do you calculate the heat change (q) for a substance given its mass, specific heat capacity (c), and temperature change (ΔT)?

Answer 6

q=m⋅c⋅ΔT
where
𝑚
m = mass,
𝑐
c = specific heat capacity,
Δ
𝑇
ΔT = temperature change.

Question 7

A compound contains 8.0 g of carbon, 1.5 g of hydrogen, and 6.0 g of oxygen. Determine the empirical formula.- how would you go about solving this?

Answer 7

-convert the masses to moles
-divide the moles by the smallest about of moles calculated
-then write the formula for it : C..H…O…. The dots with be the numbers calculated.

Question 7

How do you calculate the enthalpy change (ΔH) for a reaction using data?

Answer 7

ΔH= n/q
where
q = heat absorbed or released,
n = number of moles of the substance.

Question 8

How do you calculate and communicate measurement uncertainties in experimental data?

Answer 8

Calculate absolute uncertainties:
±errorvalue
Calculate percentage uncertainties:
absoluteuncertainty/measurement×100%
Communicate uncertainties as a range
(e.g., ±0.02).

Question 9

What is the formula to calculate the number of moles (𝑛) of a substance, and what does each variable represent?

Answer 9

molar mass= g/ moles
Context: Used in stoichiometry to relate mass and moles in chemical reactions.

Question 10

A compound has an empirical formula of CH2 and a molar mass of 56.0 g/mol. Determine the molecular formula of the compound.

Answer 10

find the molar mass of the element, so doing mm or c and mm of h tims by 2
then divide the empirical formulas MM to the actual MM.
then add brackets to element and add that number to the end of the brakcet and multiply it to the element.
eg. (CH2) 4 = c4h8 :)

Question 11

How do you calculate the percentage yield of a reaction?

Answer 11

PercentageYield=( TheoreticalYield/ExperimentalYield)×100%
Context: Used to assess the efficiency of a reaction by comparing the actual yield to the maximum possible yield.

Question 12

what is bond enthalpy

Answer 12

the amount ofenergy required to break one mole of the stated bond

Question 13

What is the formula to calculate the enthalpy change (Δ𝐻) of a reaction using bond enthalpies, and what do the terms represent?

Answer 13

ΔH=BondsBroken−BondsFormed
Context: Used to estimate the enthalpy change based on the energy required to break bonds and the energy released when new bonds are formed

Question 14

What formula is used to calculate the heat capacity of a substance, and how is it different from specific heat capacity?

Answer 14

C=m⋅c
where
C = heat capacity
m = mass
c = specific heat capacity.
Context: Heat capacity is the amount of heat needed to raise the temperature of an entire substance by 1°C. Specific heat capacity is the amount of heat needed to raise the temperature of 1 gram of a substance by 1°C

Question 15

What is the standard enthalpy change of formation, and how is it used in calculations?

Answer 15

The standard enthalpy change of formation (Δ𝐻𝑓∘ΔH f∘) is the heat change when one mole of a compound is formed from its elements in their standard states. It is used to calculate the enthalpy change of a reaction using Hess’s Law.

Question 16

How do you apply Hess’s Law (regardless of the multiple stages or steps of a reaction, the total enthalpy change for the reaction is the sum of all changes) to determine the enthalpy change of a reaction?

Answer 16

Hess’s Law states that the total enthalpy change for a reaction is the sum of the enthalpy changes for any series of steps leading to the final reaction. You can use it to calculate the enthalpy change of a reaction by combining known enthalpy changes of related reactions.

Question 17

How do you calculate the average atomic mass of an element using isotopic masses and their abundances?

Answer 17

AverageAtomicMass=
∑(isotopicmass×abundance)/totalabundance
Context: This calculation is used in mass spectrometry and to determine the weighted average mass of an element’s isotopes.

Question 18

How do ionization energies vary across periods and down groups in the periodic table?

Answer 18

Across a Period: Ionization energy increases due to increasing nuclear charge and decreasing atomic radius.
Down a Group: Ionization energy decreases due to increased atomic radius and shielding effect.

Question 19

What is the principle behind flame tests and atomic absorption spectroscopy (AAS) for identifying elements?

Answer 19

Flame Tests: Elements emit characteristic colors when heated, due to electron transitions between energy levels.
AAS: Atoms absorb specific wavelengths of light, which can be measured to identify and quantify elements in a sample.

Question 20

How do you calculate the rate of a chemical reaction using concentration and time data?

Answer 20

rate = concentration/ time

Question 21

How do ionic, covalent, and metallic bonding affect the physical properties of substances?

Answer 21

Ionic Bonding: High melting points, brittleness, conducts electricity in molten or aqueous state.
Covalent Bonding: Lower melting points, generally poor conductors, can be polar or nonpolar.
Metallic Bonding: High melting points, malleable, good conductors of heat and electricity

Question 22

What periodic trends affect atomic radius and electronegativity?

Answer 22

Atomic Radius: Decreases across a period (increased nuclear charge) and increases down a group (additional electron shells).
Electronegativity: Increases across a period (stronger attraction to electrons) and decreases down a group (increased distance from the nucleus).