Chemistry Exam 3

Do you know how to describe bond formation in Valence Bond theory?

describes covalent bonds as the overlap of half-filled atomic orbitals between two atoms, where a shared pair of electrons is formed

a. Orbital overlap: sigma (σ), pi (π) bonds

igma bonds are a result of the head-to-head overlapping of atomic orbitals whereas pi bonds are formed by the lateral overlap of two atomic orbitals

2. Within valence bond theory, can you explain hybridization?

the mixing of atomic orbitals to form new hybrid orbitals for bonding

a. sp3, sp2, sp

models for describing how atomic orbitals mix to form new hybrid orbitals for bonding

b. describe bonding: single, double, triple and hybridization of the atoms.

sp hybridization results in a linear shape with one unhybridized p orbital for a triple bond, sp2 results in a trigonal planar shape with one unhybridized p orbital for a double bond, and sp3 results in a tetrahedral shape with no unhybridized p orbitals for four single bonds

3. Given the structure of a molecule, can you assign the hybridization to each atom?

count the number of electron domains around each atom in a molecule's Lewis structure

4. Can you describe the internal motion of a molecule based on bonding, in particular single

the movements of molecules within materials

vs. multiple bonds.

higher vibrational frequencies and restricted or prevented rotation

5. Do you know an example where valence bond theory fails to describe molecular bonding?

predicting the paramagnetic nature of dioxygen and the bond angles in water

6. Do you know how to describe bond formation in Molecular Orbital theory?

atomic orbitals combining to form new, delocalized molecular orbitals that span the entire molecule

a. Orbital diagrams

visually represent the arrangement of electrons in an atom's orbitals, using boxes for orbitals and arrows for electrons to show their spin and energy levels

b. Bonds, antibonds

Electrons in bonding orbitals lower the system's energy, while electrons in antibonding orbitals increase it

c. sigma (σ), pi (π) bonds and σ* and π*

Sigma and pi bonds are two types of covalent bonds, while sigma * and pi * are antibonding orbitals that result from molecular orbital theory

d. bond order

7. Do you know how to draw a molecular orbital energy diagram for example diatomic

# of chemical bonds btwn two atoms

homonuclear and heteronuclear diatomic molecules?

Homonuclear diatomic molecules are composed of two identical atoms, like \(H_{2}\) and \(O_{2}\), while heteronuclear diatomic molecules consist of two different atoms, such as \(HCl\) and \(CO\)

8. Can you demonstrate how Molecular Orbital theory is able to prove the paramagnetism in elements like O2

A substance is paramagnetic if it is attracted to a magnetic field. This occurs because the molecule has one or more unpaired electrons

Can you describe a physical change? A chemical change?

Physical changes in matter are often reversible. Chemical changes, on the other hand, are not reversible.

Can you convert between grams and moles and vice versa?

molar mass conversion

Do you know the parts and general characteristic of a chemical equation?

the representation of reactants, products, and the reaction's direction with an arrow, and it must be balanced, meaning the number of atoms for each element is the same on both sides

Can you balance a chemical equation?

make sure the number of atoms for each element is the same on both the reactant and product sides by adding coefficients

Can you determine the mole ratio between any pair of species in a balanced chemical

equation?

look at the coefficients in your balanced equation

Can you determine the theoretical mass of a reactant required to react with a

given amount of another reactant?

first write a balanced chemical equation, convert the mass of the limiting reactant(s) to moles, use the mole ratio from the balanced equation to find the moles of product, and then convert the moles of product back into mass

Given the masses of two or more reactants, can you find the limiting reactant? The reactant that is consumed first and determines how much product can be made

first, balance the chemical equation. Then, for each reactant, use its given amount to calculate the amount of a single, specific product that could be forme

Solute

the substance being dissolved

Solvent

the substance that does the dissolving and is present in the largest amount

Can you identify and describe a nonelectrolyte, an electrolyte, a strong and weak electrolyte

Soluble ionic substances and strong acids ionize completely and are strong electrolytes, while weak acids and bases ionize to only a small extent and are weak electrolytes

Can you calculate the concentration of species (compounds, ions) in solution?

first determining the molarity of the solution and then using the mole ratio of the dissolved compound to find the concentration of each ion

Do you know how to find the concentration of a diluted solution?

using the dilution equation M1V1=M2V2

Can you predict if a compound is soluble or not?

You can predict a compound's solubility using the "like dissolves like" principle for intermolecular forces and general solubility rules for ionic compounds

Can you describe and acid-base reaction as a proton-transfer reaction

An acid-base reaction is described as a proton-transfer reaction because an acid (a Brønsted-Lowry acid) donates a proton (\(H^{+}\)) to a base (a Brønsted-Lowry base), which accepts it

Can you write a complete molecular equation?

all reactants and products shown as neutral formulas, even for soluble ionic compounds in water

Can you write the complete ionic equation?

first balance the molecular equation, then separate all soluble ionic compounds and strong acids into their constituent ions, leaving solids (s), liquids (l), and gases (g) unchanged

Can you write the net ionic equation?

you first balance the molecular equation, then write the complete ionic equation by separating aqueous compounds into ions, and finally remove the "spectator ions" (ions that appear on both sides of the arrow) to show only the reactants and products that have changed.

Can you identify spectator ions?

write out the complete ionic equation, then cross out the ions that appear in the exact same form on both the reactant and product sides

Do you know how to assign oxidation numbers to all elements in pure substances, neutral

compounds, and ionic compounds?

assigning zero to pure substances, using the element's charge for monatomic ions, and ensuring the sum of oxidation numbers equals zero for a neutral compound or the ion's charge for a polyatomic ion

Do you know how to assign oxidation numbers to all elements in pure substances, neutral

compounds, and ionic compounds

oxidation numbers are assigned to elements in pure substances using a zero oxidation number, in neutral compounds by ensuring the sum of all oxidation numbers equals zero, and in ionic compounds by assigning the oxidation number to match the charge of the monatomic ion or by using a similar sum-to-zero rule for polyatomic ions

Can you analyze a redox reaction, identify the species undergoing oxidation and reduction,

the oxidizing and reducing agent (oxidant and reductant)?

assign oxidation numbers to all atoms in the reactants and products, and identify which atoms experience a change

Can you write half reactions for simple processes?

half-reactions can be written for simple processes by splitting a redox reaction into two parts: one for oxidation (loss of electrons) and one for reduction (gain of electrons)

Do you know how to use the activity series to predict if a redox process will happen as

written or not?

A single-replacement reaction will occur if the single element is more reactive (higher on the activity series) than the element it is trying to replace in a compound

Internal energy

the total energy contained within a system, comprising the sum of all microscopic kinetic and potential energies of its molecules

Potential energy

the energy stored in the bonds of chemical compounds, which can be released or absorbed during a chemical reaction

Kinetic energy

the energy of motion that particles (atoms, molecules) possess

Heat

the heat released when a chemical reaction occurs

work

the transfer of energy that occurs when a force moves an object over a distance

-work done on a system +

-work done by system -

What are the units of energy?

joule (J), kilowatt-hours (kWh), calories (cal)

Can you define universe, system, surroundings?

the universe is the combination of the system and its surroundings

Which functions are state functions? And which are path functions?

State functions depend only on the initial and final states of a system, while path functions depend on the specific process or path taken to get from one state to another

State functions

internal energy U, enthalpy H, temperature T, pressure P, and volume V.

Path functions

Heat Q, work W

Do you know how the system and surroundings exchange energy?

primarily through heat (transfer due to temperature differences) and work (transfer through mechanical force over a distance)

Heat and work: ∆𝐸 = 𝑞 + 𝑤

first law of thermodynamics, which states that the change in a system's internal energy (\(\Delta E\)) is equal to the heat added to it (\(q\)) plus the work done on it (\(w\)).

Do you know the sign conventions for energy, heat, and work with respect to the system

and the surroundings?

Yes, energy entering a system is positive, while energy leaving the system is negative.

What is calorimetry?

The scientific process of measuring the heat absorbed or released during chemical or physical changes using a device called a calorimeter

What is the definition of specific heat? Of molar heat capacity?

the energy required to raise the temperature of one mole of a substance by one degree Celsius or Kelvin.

Can you relate the amount a substance can absorb (and the temperature it can

reach) based on its specific heat (or molar heat capacity)?

defined by the equation \(q=mc\Delta T\), where a substance's specific heat (\(c\)) directly relates the amount of heat absorbed (\(q\)) to its mass (\(m\)) and the resulting temperature change (\(\Delta T\)

Can you perform calculations for a coffee cup calorimeter problem?

calculations for a coffee cup calorimeter problem can be performed using the formula \(q=mc\Delta T\), where \(q\) is heat, \(m\) is mass, \(c\) is specific heat, and \(\Delta T\) is the change in temperature

q =H

\(q\) represents the heat transferred to or from a system, while \(H\) (or more specifically, \(\Delta H\)) represents the enthalpy change of the system.

Can you perform calculations for a bomb calorimeter problem?

To solve a bomb calorimeter problem, you first calculate the total heat absorbed by the calorimeter and its contents using the equation \(q_{cal}=C_{cal}\Delta T\), where \(C_{cal}\) is the calorimeter's heat capacity and \(\Delta T\) is the change in temperature. The heat released by the reaction (\(q_{rxn}\)) is the negative of the heat absorbed by the calorimeter, so \(q_{rxn}=-q_{cal}\).

q is E

(\(E\)) and heat (\(Q\)) is defined by the first law of thermodynamics (\(\Delta E=Q-W\)

What is enthalpy?

a thermodynamic quantity equivalent to the total heat content of a system. It is equal to the internal energy of the system plus the product of pressure and volume

Which processes are exothermic and which endothermic?

Exothermic processes release energy (like heat), causing the surroundings to get warmer. Examples include combustion and freezing. Endothermic processes absorb energy, cooling the surroundings

What is the sign of ΔH for each?

For an exothermic process, ΔH is negative because heat is released; for an endothermic process, ΔH is positive because heat is absorbed

What are standard conditions?

For an exothermic process, ΔH is negative because heat is released; for an endothermic process, ΔH is positive because heat is absorbed

What is the definition of the heat of formation, ΔHf°, of a species?

the change in enthalpy when one mole of a compound is formed from its constituent elements in their most stable standard states

Can you calculate the standard heat of a reaction (∆H°) given the heats of formation (∆Hf°)

of the reactants and products

calculate the standard heat of a reaction (\(\Delta H_{rxn}^{\circ }\)) by subtracting the sum of the standard heats of formation (\(\Delta H_{f}^{\circ }\)) of the reactants from the sum of the standard heats of formation of the products.

Multiply delta H by a factor

multiply the \(\Delta H\) value by the same factor you used to multiply the chemical equation

Swap reactants and products

swapping reactants and products, the sign of the enthalpy change (\(\Delta \)H) is reversed

Add two or more processes

their individual enthalpy changes (\(\Delta H\) values) are also added to find the net enthalpy change of the overall process

Do you know how to apply Hess’s Law?

you manipulate a series of chemical reactions with known enthalpy changes (\(\Delta H\)) so that when you add them together, they produce the overall reaction you want to find the enthalpy for

From amounts and standard heat of reaction (∆H°), can you find ∆H?

overall enthalpy change (\(\Delta H\)) of a reaction from the amounts (moles) of reactants and products and the standard heat of reaction (\(\Delta H^{\circ }\)). This is done by using the formula: \(\Delta H^{\circ }=\sum \Delta H_{f}^{\circ }(\text{products})-\sum \Delta H_{f}^{\circ }(\text{reactants})\)

Can you predict lattice energy based on ionic charge and size of the ions?

can be predicted based on ionic charge and size, with higher charges and smaller ion sizes leading to higher lattice energy.

Do you understand how the magnitude of lattice energy affects solubility?

a higher lattice energy generally leads to lower solubility because more energy is required to break the ionic bonds in the crystal lattice.

Can you estimate reaction enthalpy based on bond energies?

calculating the difference between the energy required to break bonds in the reactants and the energy released when new bonds form in the products