Chemistry: Chemical Bonding, Equilibrium, Energetics, and Group 2 Trends

Flashcards covering molecular geometry, bonding types, electronegativity trends, Le Chatelier's principle, Group 2 chemical trends, enthalpy definitions, Hess' law, and atom economy calculations based on the lecture notes.

What is the bond angle and shape for a molecule with 2 bonding pairs?

Linear with a bond angle of $180^{\circ}$

What are the characteristics of a molecule with 3 bonding pairs according to the notes?

Shape: trigonal pianar; Angle: $120^{\circ}$

What is the shape and bond angle for a molecule with 4 bonding pairs?

te trane dra with an angle of $109.5^{\circ}$

Describe the bond angles and shape for 5 bonding pairs.

trigonal bipyramid with angles of $120^{\circ}$ and $90^{\circ}$

What is the shape and angle for 6 bonding pairs?

Octanederal with a bond angle of $90^{\circ}$

How do lone pairs affect bonding pairs in terms of repulsion?

Lone pairs repel even further than bonding pairs, which forces bonds closer together.

What is electronegativity?

The ability of an atom to attract electrons towards itself in a covalent bond.

According to the Pauung Scale, what are the most electonegative elements?

FON (Fluorine, Oxygen, and Nitrogen)

What are the trends for electronegativity on the periodic table?

It increases across a period and decreases down a group.

Under what conditions do ionic compounds conduct electricity?

Only when molten or dissolved, because the electrons are free to move.

What is a coordinate (dative) covalent bond?

A covalent bond where one atom donates both electrons, represented with an arrow.

Define dynamic equilibrium.

A state in a closed system where the rate of the forward and backward reaction becomes equal and concentrations remain unchanging.

State Le chatlier's Principle.

If a change is made to the conditions of equilibrium, equilibrium will shift in the direction that opposes the disruption.

What is the formula for the equilibrium constant $K_c$ for the reaction $A + B \rightleftharpoons C + D$?

$$K_c = \frac{[C][D]}{[A][B]}$$

What are the compromise conditions for the Haber process ($N_2(g) + 3H_2(g) \rightleftharpoons 2NH_3(g)$, $\Delta H = -92\,kJ$)?

Mid temperature (to balance yield and speed), high pressure (shifts equilibrium right), and an Iron catalyst.

What is the solubility trend for Group 2 hydroxides down the group?

Solubility increases down the group as the larger ionic radius leads to weaker attraction between metal ions and hydroxides.

What is the solubility trend for Group 2 sulfates down the group?

Solubility decreases down the group; $BaSO_4$ is the least soluble.

What is the test for sulfate ($SO_4^{2-}$) ions?

Add $HNO_3$ to neutralize, then add $BaCl_2$ to check for a white precipitate of $BaSO_4$.

Define standard enthalpy of formation ($\Delta_f H$).

The enthalpy change when $1\,mol$ of a compound is formed from its elements in standard states under standard conditions.

What is Hess' law?

The enthalpy change of a reaction is independent of the route taken, provided reactants and products are under standard conditions.

How is the heat change ($q$) calculated in calorimetry?

$q = mc\Delta T$, where $m$ is mass of $H_2O$, $c$ is specific heat, and $\Delta T$ is temperature change.

What is the formula for Percentage Atom Economy?

$$\% \text{ Atom Economy} = \frac{\text{molecular mass of desired product}}{\text{sum of molecular masses of all reactants}} \times 100$$

What is the mean bond enthalpy of a $C-H$ bond if the total energy to break 4 bonds in methane ($CH_4$) is $1662\,kJ$?

$$415.5\,kJ\,mol^{-1}$$

How is enthalpy change calculated using mean bond enthalpies?

$$\Delta H = \text{Total energy to break bonds} - \text{Total energy released forming bonds}$$