Energy, rates, equilibrium, acids, cells and solutions

Grade 12 Chemistry

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Thermochemistry

L1
Lesson 1
Counting particles
grams → moles → molecules, before any heat arrives
Thermochemistry measures energy PER MOLE, so every problem this chapter opens the same way: turn what you weighed into what you counted.
The formula in this lesson
$n = \dfrac{m}{M}$
Start
L2
Lesson 2
Heat in the cup
ΔT is a difference, not a reading
The Greek delta is said delta, and it means final minus initial — always in that order, every time it appears. Two consequences of that order, and the exam lives on both.
The formula in this lesson
$Q = m c \Delta T$
Start
L3
Lesson 3
Warming and melting
the heating curve · slopes take mcΔT, plateaus take mL
Heat a beaker of ice steadily and plot temperature against time. The graph is not a ramp — it is a staircase of slopes and plateaus, and each kind of segment has its own machine.
The formulas in this lesson
$Q = m L$ , $Q = m c \Delta T$
Start
L4
Lesson 4
Heat per mole
Why exothermic is negative
A calorimeter reports joules. A data table reports kilojoules per mole.
The formula in this lesson
$q = n\,\Delta H$
Start
L5
Lesson 5
The coffee cup
two formulas in one chain · heat from the water, moles from the solution
A coffee-cup calorimeter is a polystyrene cup, a lid and a thermometer, and it measures enthalpy changes by refusing to let heat escape.
The formula in this lesson
$Q = m c \Delta T$
Start
L6
Lesson 6
The ladder of Hess
route a reaction through steps you already know
Some reactions cannot be run cleanly in a calorimeter — you cannot burn carbon and get pure carbon monoxide, and nobody makes acetylene from graphite by asking nicely.
The formula in this lesson
$\Delta H_{\text{rxn}} = \Delta H_1 + \Delta H_2 + \Delta H_3$
Start
L7
Lesson 7
The formation shortcut
ΔH°f tables · products minus reactants, in that order
Routing every reaction by hand would be exhausting, so chemistry tabulated the routes once.
The formula in this lesson
$\Delta H^{\circ}_{\text{rxn}} = \sum \Delta H^{\circ}_{f}(\text{prod}) - \sum \Delta H^{\circ}_{f}(\text{react})$
Start
★
Boss lesson
The Heat Audit
the boss · no calculator · mass to moles to a verdict
One pellet, one long problem, and every answer feeds the next: grams to moles, moles to kilojoules, kilojoules to joules, joules to a temperature rise — and then the line that actually matters, whether the run passes its specification.
Start

Rates & Kinetics

L9
Lesson 9
Reading the rate law
the order is an exponent you MEASURE
Equilibrium asked where a reaction ends up. Kinetics asks something the balanced equation cannot answer: how FAST it gets there.
The formula in this lesson
$r = k\,[\mathrm{A}]^{n}$
Start
L10
Lesson 10
Arrhenius and the hill
Kelvin only, joules only
Molecules collide constantly and mostly bounce. A reaction happens only when a collision arrives with enough energy to climb the activation energy — the hill between reactants and products.
The formula in this lesson
$k = A\,e^{-E_a/RT}$
Start
L11
Lesson 11
Two temperatures
Ea from a pair of runs — or from the plot's slope
Let the units keep you honest one way only — if they refuse to cancel into J/mol the rearrangement is wrong, no appeal; units that do work out never prove you right.
The formulas in this lesson
$\ln\dfrac{k_2}{k_1} = \dfrac{E_a}{R}\left(\dfrac{1}{T_1} - \dfrac{1}{T_2}\right)$ , $E_a = -R \times \text{slope}$
Start
L12
Lesson 12
Straight-line decay
zero order falls in a line, first order in a curve
A rate law tells you the speed right now. Integrate it over a clock and you get the concentration ITSELF at any time — an integrated rate law.
The formulas in this lesson
$[\mathrm{A}] = [\mathrm{A}]_0 - kt$ , $[\mathrm{A}] = [\mathrm{A}]_0\,e^{-kt}$
Start
L13
Lesson 13
The half-life clock
Then count the halvings
Ask a first-order reaction how long it takes to lose HALF of itself and something remarkable falls out.
The formulas in this lesson
$t_{1/2} = \dfrac{\ln 2}{k}$ , $N = N_0\left(\tfrac{1}{2}\right)^{t/t_{1/2}}$
Start
L14
Lesson 14
Second-order slowdown
1/[A] climbs · and every half-life is longer than the last
A second-order step needs two molecules in the same place at the same instant. As the reactant thins, those meetings get rare fast — so a second-order reaction does not just slow down, it slows down and then slows down again.
The formulas in this lesson
$\dfrac{1}{[\mathrm{A}]} = \dfrac{1}{[\mathrm{A}]_0} + kt$ , $t_{1/2} = \dfrac{1}{k\,[\mathrm{A}]_0}$
Start
★
Boss lesson
The Rate Tribunal
the boss · no calculator · read it, warm it, run the clock
One tank, one long problem, and every answer feeds the next: the rate constant from the logged rate, then the warmed constant, then the half-life it buys, then what survives the hold — and finally the only thing the plant actually cares…
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Chemical Equilibrium

L16
Lesson 16
Writing K
products over reactants — and who never shows up
A reversible reaction does not stop; it gets BORED. Forward and reverse settle at the same speed, the concentrations stop drifting, and the mixture sits there looking still while both reactions run flat out underneath.
The formula in this lesson
$K_c = \dfrac{[\mathrm{C}][\mathrm{D}]}{[\mathrm{A}][\mathrm{B}]}$
Start
L17
Lesson 17
Q against K
the same expression, measured too early — and what it predicts
Here is the trick that makes equilibrium predictive rather than merely descriptive.
The formula in this lesson
$Q = \dfrac{[\mathrm{C}]^{c}}{[\mathrm{A}]^{a}[\mathrm{B}]^{b}}$
Start
L18
Lesson 18
Kp meets Kc
(RT)^Δn · the crossing from concentrations to pressures
Gases can be counted two ways: by concentration in mol/L, or by the pressure they push with. The ideal gas law joins them in one line.
The formulas in this lesson
$K_p = K_c (RT)^{\Delta n}$ , $K_c = \dfrac{K_p}{(RT)^{\Delta n}}$
Start
L19
Lesson 19
Sparingly soluble
Ksp · s² against 4s³ · and why the smaller Ksp can win
Drop a spoon of silver chloride into water and almost nothing dissolves — but not NOTHING.
The formulas in this lesson
$K_{sp} = 4s^{3}$ , $K_{sp} = s^{2}$
Start
L20
Lesson 20
Gibbs decides
ΔG = ΔH − TΔS, and the bridge ΔG° = −RT ln K
Two urges argue in every reaction. Energy wants to go downhill — that is enthalpy. Matter wants to spread out — that is entropy.
The formulas in this lesson
$\Delta G = \Delta H - T\,\Delta S$ , $\Delta G^{\circ} = -RT\ln K$
Start
★
Boss lesson
The Position of Equilibrium
the boss · no calculator · one converter, every tool in the chapter
Chemists have used that shortcut for a century; today you get to.
Start

Acids & Bases

L22
Lesson 22
The pH scale
p is an operator · pH, pOH, and the ruler they share
Grade 11 taught you to read a pH. Grade 12 asks what the symbol MEANS, because the same move is about to be played on four other quantities.
The formulas in this lesson
$\mathrm{pH} = -\log[\mathrm{H^+}]$ , $\mathrm{pH} + \mathrm{pOH} = 14$
Start
L23
Lesson 23
The Kw family
Ka, Kb, Kw · and the p-scale that flattens them
Those two are not independent.
The formulas in this lesson
$\mathrm{p}K_a = -\log K_a$ , $K_a K_b = K_w$ , $\mathrm{p}K_a + \mathrm{p}K_b = 14$
Start
L24
Lesson 24
Weak acids and ICE
pH from Ka and C · and how much actually let go
Put a weak acid in water and set up an ICE table — Initial, Change, Equilibrium. Call the formal concentration C: the amount you actually made up, in mol/L, before any proton moved.
The formulas in this lesson
$\mathrm{pH} = -\tfrac{1}{2}\log(K_a C)$ , $\%\,\mathrm{ion} = \dfrac{[\mathrm{H^+}]}{C} \times 100\%$
Start
L25
Lesson 25
Buffer country
Henderson–Hasselbalch · the pair's ratio sets the pH
A buffer holds a weak acid AND its conjugate base in the same flask, so acid added is mopped up by the base and base added is mopped up by the acid.
The formulas in this lesson
$\mathrm{pH} = \mathrm{p}K_a + \log\dfrac{[\mathrm{A^-}]}{[\mathrm{HA}]}$ , $\mathrm{pOH} = \mathrm{p}K_b + \log\dfrac{[\mathrm{BH^+}]}{[\mathrm{B}]}$
Start
L26
Lesson 26
Dilution discipline
Final volume, never added volume
Not the volume of solvent you poured: the volume of what is in the flask when you stop.
The formulas in this lesson
$C = \dfrac{n}{V}$ , $C_1 V_1 = C_2 V_2$
Start
L27
Lesson 27
The burette
titration · the mole ratio referees · mL cancels, until it doesn't
A titration measures a concentration you cannot see by reacting it away against one you can. A pipetted aliquot of the unknown acid waits in the flask; standard base drips from the burette until the indicator turns.
The formula in this lesson
$C_a V_a = n\,C_b V_b$
Start
★
Boss lesson
The Titration Final
the boss · no calculator · dilute it, titrate it, then rule on it
One bench runs the whole unit: the volumetric flask dilutes the titrant, the burette finds the acid, the log places it on the scale, the see-saw hands over the other end — and every answer feeds the next line.
The formula in this lesson
$C_1 V_1 = C_2 V_2$
Start

Electrochemistry

L29
Lesson 29
Reading the table
which half-cell is the cathode, and what the cell is worth
Every electrochemistry data sheet you will ever be handed prints its half-reactions as reductions — electrons on the left, going in.
The formula in this lesson
$E^{\circ}_{\text{cell}} = E^{\circ}_{\text{cat}} - E^{\circ}_{\text{an}}$
Start
L30
Lesson 30
Nernst, off standard
what the cell is worth once the bath drifts
A real cell leaves those conditions the instant it starts working — it eats its reactants.
The formula in this lesson
$E = E^{\circ} - \dfrac{0.0592}{n}\log Q$
Start
L31
Lesson 31
Charge on the clock
The seconds the formula insists on
An ampere is not a substance that flows; it is a rate. One ampere is one coulomb per second.
The formula in this lesson
$Q = It$
Start
L32
Lesson 32
Faraday's scales
Coulombs weighed as grams
Name every letter before it works. m is the mass deposited at the electrode, in grams. Q is the charge passed, in coulombs. M is the molar mass of the element plating out, in grams per mole. F is the Faraday constant, 96500 C/mol — the…
The formula in this lesson
$m = \dfrac{QM}{nF}$
Start
L33
Lesson 33
Time to plate
the full ladder · mass, current or clock in turn
A plating shop never asks for a mass. It asks for a setting: how many amperes, for how many minutes, to land the thickness the drawing calls for.
The formulas in this lesson
$m = \dfrac{QM}{nF}$ , $Q = It$
Start
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Boss lesson
The Electroplating Shift
the boss · no calculator · size the cell, run the current, weigh the rack
No calculator. F = 96500 C/mol, and every draw is pinned so the coulombs land on a clean fraction of a mole of electrons — 0.300, 0.600, numbers you can carry in your head from one line to the next.
Start

Gases & Solutions

L35
Lesson 35
The three gas laws
one knob at a time · Boyle, Charles, Gay-Lussac
A fixed amount of gas has three knobs: pressure P, how hard it drums on its walls; volume V, the space it is allowed to fill; and temperature T, the average kinetic energy of its molecules.
The formulas in this lesson
$P_1 V_1 = P_2 V_2$ , $\dfrac{V_1}{T_1} = \dfrac{V_2}{T_2}$ , $\dfrac{P_1}{T_1} = \dfrac{P_2}{T_2}$
Start
L36
Lesson 36
Combined and ideal
several knobs at once · PV = nRT · 22.4 L/mol
Same fixed amount of gas, same subscript convention (1 before, 2 after), and now any of the three knobs may move. Pin any one of them and the matching pair cancels, handing you Boyle, Charles or Gay-Lussac back.
The formulas in this lesson
$\dfrac{P_1 V_1}{T_1} = \dfrac{P_2 V_2}{T_2}$ , $PV = nRT$ , $V = n\,V_m$
Start
L37
Lesson 37
Molar mass from the gas
Weigh a litre, name the gas
Two definitions meet here.
The formula in this lesson
$\rho = \dfrac{PM}{RT}$
Start
L38
Lesson 38
Partial pressures
Dalton's law · a share of the moles is a share of the pressure
Ideal gas molecules ignore each other. Put two gases in one vessel and each behaves exactly as if it owned the place, so the pressures simply add — that is Dalton's law of partial pressures.
The formula in this lesson
$P_i = x_i\,P_{\text{total}}$
Start
L39
Lesson 39
Graham's race
lighter is faster — but only by a square root
Temperature is average kinetic energy.
The formula in this lesson
$\dfrac{r_1}{r_2} = \sqrt{\dfrac{M_2}{M_1}}$
Start
L40
Lesson 40
Three ways to say how much
molarity · molality · mass percent
Three measures, three denominators, and the denominator is the whole story.
The formulas in this lesson
$C = \dfrac{n}{V}$ , $b = \dfrac{n}{m_{\text{solvent}}}$ , $c = \dfrac{m_{\text{solute}}}{m_{\text{solution}}} \times 100\%$
Start
L41
Lesson 41
Colligative counting
ΔTb, ΔTf and Π · the solute's identity never matters
A colligative property depends on HOW MANY solute particles are dissolved and not at all on what they are — the word shares a root with “collect”.
The formulas in this lesson
$\Delta T_f = K_f\,b$ , $\Delta T_b = K_b\,b$ , $\Pi = MRT$
Start
L42
Lesson 42
Vapour pressure stories
Raoult · Henry · Clausius–Clapeyron
Above every liquid sits a vapour, and three laws tell you how much.
The formulas in this lesson
$P = x\,P^{0}$ , $C = H P$ , $\ln\!\left(\dfrac{P_2}{P_1}\right) = -\dfrac{\Delta H_{vap}}{R}\left(\dfrac{1}{T_2} - \dfrac{1}{T_1}\right)$
Start
★
Boss lesson
The Gas Works
the boss · no calculator · compress it, mix it, weigh it
No calculator — every draw is pinned to mental arithmetic, and the standard state does the heavy lifting: at STP one mole fills 22.4 L, and the compressor's pressures and temperatures are whole multiples of 101 kPa and 273 K, so the…
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