CAIE A2 Level Chemistry (9701) - Chemical Energetics Flashcards

A set of 15 practice flashcards based on the CAIE A2 Level Chemistry lecture notes on Chemical Energetics, covering enthalpy changes, lattice energy, electron affinity, and Group 2 solubility trends.

What is the definition of the Enthalpy Change of Atomisation ($\Delta H_{at}^{\ominus}$)?

The enthalpy change measured when $1\text{ mole}$ of gaseous atoms is formed from its element under standard conditions.

How is Lattice Energy ($\Delta H_{lat}^{\ominus}$) defined?

The enthalpy change when $1\text{ mole}$ of an ionic compound is formed from its gaseous ions under standard conditions.

Why is Lattice Energy always exothermic ($-ve$)?

Because cations attract anions and energy is released when bonds are formed.

What is indicated if the theoretical and experimental values for Lattice Energy are similar?

The bonding in the compound is pure ionic; otherwise, it is an intermediate between ionic and covalent.

How does the radius of an ion affect Lattice Energy?

A smaller radius results in a greater charge density and stronger electrostatic forces, making $\Delta H_{lat}^{\ominus}$ more exothermic.

What is the definition of the First Electron Affinity ($\Delta H_{ea}^{\ominus}$)?

The enthalpy change when $1\text{ mole}$ of electrons is added to $1\text{ mole}$ of gaseous atoms to form $1\text{ mole}$ of mononegative gaseous anions under standard conditions.

Why are the second and third electron affinities endothermic?

Because when an electron is added to a $-ve$ ion, repulsion is present and energy is required to force the electron into the ion.

According to the trends for Groups 16 and 17, how does Electron Affinity (E.A.) change down the group?

After the first element, electron affinity becomes less exothermic (less negative) down the group.

What formula expresses the relationship between enthalpy of hydration, lattice energy, and enthalpy of solution?

$$\Delta H_{hyd}^{\ominus} = \Delta H_{lat}^{\ominus} + \Delta H_{sol}^{\ominus}$$

How does the transcript define Ion Polarisation?

The distortion of the electron cloud on an anion by a neighbouring cation.

What two factors increase the polarising power of a cation?

High positive charge and small size (high charge density).

What is the order of thermal stability for Group 2 cations?

$$Ba^{2+} > Sr^{2+} > Ca^{2+} > Mg^{2+}$$

Why does the thermal stability of Group 2 nitrates and carbonates increase down the group?

As the size of the cation increases, polarising power decreases, leading to less distortion of the anion and higher decomposition temperatures.

According to the notes, why does the solubility of Group 2 Hydroxides increase down the group?

Because $\Delta H_{sol}^{\ominus}$ becomes more exothermic as the decrease in $\Delta H_{lat}^{\ominus}$ is less than the decrease in $\Delta H_{hyd}^{\ominus}$.

Why does the solubility of Group 2 Sulfates decrease down the group?

Because $\Delta H_{sol}^{\ominus}$ becomes less exothermic as the decrease in $\Delta H_{lat}^{\ominus}$ is less than the decrease in $\Delta H_{hyd}^{\ominus}$.