energetics

What is ionic bonding in simple terms?

Ionic bonding involves the transfer of electrons from metal atoms to non-metal atoms, forming positively charged metal ions and negatively charged non-metal ions that have stable outer electron shells.

How do ions arrange themselves in ionic bonding?

Ions arrange themselves into a lattice structure where ions of opposite charge are adjacent to each other due to their attractive forces.

What is the significance of the Born-Haber cycle in ionic bonding?

Born-Haber cycles are used to calculate lattice enthalpies indirectly, as they account for all enthalpy changes involved in the formation of an ionic compound.

What is the starting point for constructing a Born-Haber cycle?

Born-Haber cycles start with the elements in their standard states, which have zero enthalpy by definition.

What is the enthalpy change associated with the formation of a solid ionic compound in a Born-Haber cycle?

The enthalpy of formation of the solid ionic compound is negative, indicating an exothermic process.

What are the steps involved in a Born-Haber cycle?

1. Elements in standard states at 0 enthalpy. 2. Atomisation of metal (positive, uphill). 3. Atomisation of non-metal (positive, uphill). 4. Ionisation energy of metal (positive, uphill). 5. Electron affinity of non-metal (negative, downhill). 6. Lattice enthalpy of formation.

What is the example used to illustrate a Born-Haber cycle?

Sodium chloride (NaCl) is used as an example, detailing the steps from standard states to lattice formation.

What additional steps are needed for Born-Haber cycles involving Group 2 elements?

For Group 2 elements like Mg, both the first and second ionisation energies must be considered, and the first electron affinity must be doubled for the negative ion.

What should you remember when doing Born-Haber cycles for elements with a charge of 2?

For a Group 2 metal, include both ionisation energies; for a Group 6 element with a 2- charge, include both first and second electron affinities.

How do you calculate enthalpy of formation in ionic compounds?

Enthalpy of formation equals the sum of all other enthalpy values: atomisations + ionisations + electron affinities + lattice enthalpy of formation.

What is the formula for calculating lattice enthalpy of formation?

Lattice enthalpy of formation = enthalpy of formation - (sum of all other enthalpy changes).

What does the lattice enthalpy of a compound indicate?

The lattice enthalpy indicates the strength of the ionic bonding within the compound.

What is the relationship between lattice enthalpy and ionic bonding strength?

Higher lattice enthalpy corresponds to stronger ionic bonding.

What is the enthalpy change for atomisation in a Born-Haber cycle?

The enthalpy change for atomisation is positive, indicating energy is required to convert solid atoms into gaseous atoms.

What is the enthalpy change for electron affinity in a Born-Haber cycle?

The enthalpy change for electron affinity is negative, indicating energy is released when a non-metal atom gains an electron.

What is the significance of the lattice formation enthalpy in ionic compounds?

Lattice formation enthalpy represents the energy released when gaseous ions combine to form a solid ionic compound.

What does the term 'atomisation' refer to in the context of Born-Haber cycles?

Atomisation refers to the process of converting a solid metal or non-metal into gaseous atoms.

What is the role of ionisation energy in Born-Haber cycles?

Ionisation energy represents the energy required to remove electrons from metal atoms to form gaseous metal ions.

What happens to the enthalpy of formation when calculating ionisation energy?

Ionisation energy can be calculated by rearranging the enthalpy of formation equation: An ionisation energy = enthalpy of formation - (sum of all other enthalpy changes).

What is the significance of the negative sign in the enthalpy of formation for ionic compounds?

The negative sign indicates that the formation of the ionic compound is an exothermic process, releasing energy.

What do you need to account for when calculating electron affinities for ions with multiple moles?

For ions with a charge of 2, account for both first and second electron affinities, while for single negative charges, only the first electron affinity is needed.

What does a greater magnitude of lattice enthalpy indicate?

Stronger bonding between ions.

What factors affect lattice enthalpy?

The size of ions and the charge of ions.

How do smaller ions affect lattice enthalpy?

Smaller ions lead to greater lattice enthalpy due to increased electrostatic attraction.

What is the relationship between ionic charge and lattice enthalpy?

Higher charges on ions result in greater attraction and thus greater lattice enthalpy.

What is required to dissolve an ionic compound in a solvent?

The ionic lattice must be broken, which requires energy input known as lattice enthalpy.

What happens to ions when an ionic compound dissolves in water?

The ions are solvated, with positive ions surrounded by negative ends of water dipoles and negative ions surrounded by positive ends.

How does the enthalpy change of hydration relate to lattice enthalpy?

It shows similar trends; it is more negative for highly charged ions and less negative for larger ions.

What are the three processes involved in dissolving an ionic compound in water?

1. Breaking the ionic lattice (lattice dissociation enthalpy), 2. Hydrating cations (enthalpy of hydration), 3. Hydrating anions (enthalpy of hydration).

What is the formula for calculating solution enthalpies?

ΔsolutionHo = Δlattice enthalpy dissociationHo + ΣΔhydrationHo.

What is the sign of lattice enthalpy of dissociation?

Always positive.

What is the sign of enthalpy of hydration?

Always negative.

What does a negative ΔsolHo indicate?

An exothermic process that heats up the solution.

What does a positive ΔsolHo indicate?

An endothermic process that cools down the solution.

How is theoretical lattice enthalpy calculated?

Using a Born-Haber cycle considering size, charge, and arrangement of ions.

What assumptions are made in theoretical lattice enthalpy calculations?

All ions are spherical and have evenly distributed charges, assuming perfect ionic character.

What causes differences between experimental and theoretical lattice enthalpy values?

The presence of covalent character due to distortion of ions.

What is covalent character in ionic compounds?

It occurs when ions are distorted, leading to non-symmetrical charge distribution.

Which ions are better at distorting negative ions?

Small and/or highly charged positive ions (cations).

Which ions are easier to polarize?

Large and/or highly charged negative ions (anions).

What is the effect of covalent character on solubility in water?

Ionic compounds with covalent character often have low solubility or are insoluble.

How does the difference between experimental and theoretical lattice enthalpy values relate to ionic character?

A larger difference indicates greater covalent character, while a smaller difference suggests almost spherical ions.

What can be inferred if the experimental value of lattice enthalpy is significantly different from the theoretical value?

The compound likely has some covalent character due to distorted ions.

What happens to the shape of ions in a compound when the difference in charge is small?

The compound will have almost spherical ions.

What is the definition of a feasible and spontaneous reaction?

A reaction that has a tendency to happen naturally, without external work being needed.

What does enthalpy change (ΔH) fail to explain about some reactions?

It does not explain why a number of endothermic reactions are spontaneous.

What is activation energy in a chemical reaction?

The energy required for bond breaking, which is endothermic.

What is the relationship between bond making and energy?

Bond making is exothermic.

How is entropy (S) defined in thermodynamics?

Entropy is the measurement of the disorder or randomness of a system.

What is the unit of measurement for entropy?

J K-1 mol-1.

What does the 2nd law of thermodynamics state about entropy?

Over time, entropy will naturally increase.

How is entropy change (∆S) calculated?

∆S = ΣSproducts - ΣSreactants.

What is the significance of 0 entropy?

0 entropy represents a perfect system.

What does the 3rd law of thermodynamics state about entropy at absolute zero?

The entropy of a substance is zero at absolute zero.

How does temperature affect the entropy of a substance?

Entropy increases with temperature as particles vibrate/move faster.

Which state of matter has the most entropy?

Gases have the most entropy due to rapid and random particle movement.

What is Gibbs free energy change (∆G) and its formula?

∆G combines enthalpy change (∆H) and entropy change (∆S) and is calculated as ∆G = ∆H - (T x ∆S/1000).

What does a negative Gibbs free energy (∆G) indicate about a reaction?

If ∆G is less than or equal to zero, the reaction is feasible.

How does Gibbs free energy vary with temperature?

∆G depends on temperature due to the term T∆S, affecting feasibility.

What happens to ∆G when there is a positive value for ∆S?

A positive value for ∆S makes ∆G more negative.

What is the significance of the temperature at which ∆G = 0?

It is the point at which the reaction is just feasible.

What does it mean for a substance to be thermodynamically unstable?

It means the reaction does not occur under standard temperature.

What is the relationship between kinetics and thermodynamics in terms of stability?

A substance can be kinetically stable if the reaction occurs at higher temperatures.