Engineering and Science Admissions Test (ESAT) Chemistry Module Syllabus

State the formula linking moles, mass and molar mass.

$$n = \frac{m}{M}$$ where $n$ = moles, $m$ = mass (g), $M$ = molar mass ($\text{g mol}^{-1}$).

Define empirical formula and molecular formula.

Empirical formula: the simplest whole-number ratio of atoms of each element in a compound. Molecular formula: the actual number of atoms of each element in a molecule (a whole-number multiple of the empirical formula).

How is percentage yield calculated?

$$\%\text{ yield} = \frac{\text{actual yield}}{\text{theoretical yield}} \times 100$$

How is atom economy calculated and why is high atom economy desirable?

$$\%\text{ atom economy} = \frac{M_r\,(\text{desired product})}{M_r\,(\text{all reactants})} \times 100$$ High atom economy means less waste, more sustainable and economical use of raw materials.

What is concentration and what equation links it to moles and volume?

Amount of solute per unit volume of solution. $$c = \frac{n}{V}$$ with $c$ in $\text{mol dm}^{-3}$, $n$ in mol, $V$ in $\text{dm}^{3}$ ($1\ \text{dm}^{3} = 1000\ \text{cm}^{3}$).

State the molar volume of a gas at room temperature and pressure (RTP) and the formula using it.

At RTP, one mole of any gas occupies $24\ \text{dm}^{3}$ ($24000\ \text{cm}^{3}$). $$n = \frac{V}{24}\quad (V \text{ in dm}^{3})$$

State the ideal gas equation, defining each term with SI units.

$$pV = nRT$$ $p$ = pressure (Pa), $V$ = volume ($\text{m}^{3}$), $n$ = moles, $R = 8.31\ \text{J K}^{-1}\text{mol}^{-1}$, $T$ = temperature (K). Convert $^{\circ}\text{C}$ to K by adding $273$.

Outline how a titration determines an unknown concentration.

Titrate a known volume of one solution against a standard solution using an indicator to find the equivalence point. Use $n=cV$ and the equation's mole ratio to find the unknown concentration: $$c_{unknown}=\frac{n_{unknown}}{V_{unknown}}$$

Define oxidation and reduction in terms of electrons and oxidation number.

Oxidation = loss of electrons / increase in oxidation number. Reduction = gain of electrons / decrease in oxidation number (OIL RIG). They occur together in a redox reaction.

What is a neutralisation reaction, and what is the general ionic equation?

Reaction of an acid with a base/alkali to form a salt and water. Ionic equation: $$\ce{H+ + OH- -> H2O}$$

Give the general products of acid + metal, acid + carbonate, and acid + metal oxide.

Acid + metal $\rightarrow$ salt + hydrogen. Acid + carbonate $\rightarrow$ salt + water + carbon dioxide. Acid + metal oxide $\rightarrow$ salt + water.

Distinguish exothermic and endothermic reactions, including the sign of $\Delta H$.

Exothermic: releases heat to surroundings, $\Delta H < 0$ (negative), products lower in energy. Endothermic: absorbs heat, $\Delta H > 0$ (positive), products higher in energy.

What is activation energy ($E_a$) and how is it shown on a reaction profile?

The minimum energy colliding particles must have to react. On a reaction profile it is the energy difference (hump) between the reactants and the peak of the curve (the transition state).

State the equation for calculating enthalpy change from bond energies.

$$\Delta H = \sum E(\text{bonds broken}) - \sum E(\text{bonds formed})$$ Breaking bonds is endothermic; forming bonds is exothermic.

State the equation for heat energy transferred when a substance changes temperature.

$$q = mc\Delta T$$ $q$ = heat (J), $m$ = mass (g), $c$ = specific heat capacity ($\text{J g}^{-1}\text{K}^{-1}$), $\Delta T$ = temperature change (K or $^{\circ}\text{C}$).

What happens at the cathode and anode during electrolysis?

Cathode (negative electrode): positive ions (cations) gain electrons and are reduced. Anode (positive electrode): negative ions (anions) lose electrons and are oxidised.

In the electrolysis of molten lead(II) bromide, write the electrode half-equations.

Cathode: $$\ce{Pb^2+ + 2e- -> Pb}$$ Anode: $$\ce{2Br- -> Br2 + 2e-}$$

For electrolysis of aqueous solutions, what rules decide the products at each electrode?

Cathode: hydrogen is released unless the metal is less reactive than hydrogen (then the metal forms). Anode: oxygen is released unless a halide ion is present (then the halogen forms).

State collision theory and the two conditions for a successful collision.

Particles must collide for a reaction to occur. A successful (effective) collision requires the particles to collide (1) with energy $\geq$ the activation energy and (2) in the correct orientation.

List four factors that increase the rate of reaction and the reason for each.

Higher temperature (more energy, more frequent successful collisions); higher concentration/pressure (more particles per volume, more collisions); larger surface area (more exposed particles); catalyst (lowers $E_a$).

How does a catalyst speed up a reaction without being used up?

It provides an alternative reaction pathway with a lower activation energy, so a greater proportion of collisions are successful. It is regenerated and not consumed overall.

What is dynamic equilibrium in a reversible reaction?

In a closed system, the forward and reverse reactions occur at equal rates, so the concentrations of reactants and products remain constant (though both reactions continue).

State Le Chatelier's principle.

If a system at equilibrium is subjected to a change in conditions (concentration, pressure, or temperature), the position of equilibrium shifts to oppose (counteract) that change.

Using Le Chatelier's principle, how does increasing temperature affect an exothermic equilibrium?

The equilibrium shifts in the endothermic (reverse) direction to absorb the added heat, reducing the yield of product and decreasing $K_c$.

State the conditions used in the Haber process and its equation.

$$\ce{N2(g) + 3H2(g) <=> 2NH3(g)}$$ Conditions: about $450\,^{\circ}\text{C}$, $200\ \text{atm}$, and an iron catalyst — a compromise for acceptable yield and rate.

What is the general formula of alkanes and why are they relatively unreactive?

$C_nH_{2n+2}$. They are saturated (only single $\ce{C-C}$ and $\ce{C-H}$ bonds), which are strong and non-polar, so alkanes are unreactive except in combustion and substitution.

Give the general formula of alkenes and the test that distinguishes them from alkanes.

$C_nH_{2n}$ (one $\ce{C=C}$ double bond, unsaturated). Test: alkenes decolourise orange bromine water; alkanes do not.

Name the functional groups of alcohols, carboxylic acids and esters.

Alcohol: hydroxyl, $\ce{-OH}$. Carboxylic acid: carboxyl, $\ce{-COOH}$. Ester: $\ce{-COO-}$ (formed from an alcohol + carboxylic acid).

Define addition polymerisation and give the equation pattern for poly(ethene).

Many unsaturated monomers join via their double bonds with no other product. $$\ce{n\,CH2=CH2 -> \,-(CH2-CH2)_n-}$$

How does condensation polymerisation differ from addition polymerisation?

Condensation joins monomers (each with two functional groups) with the loss of a small molecule (usually $\ce{H2O}$) at each link; addition uses unsaturated monomers and loses nothing. Polyesters and polyamides are condensation polymers.

State the flame test colours for lithium, sodium, potassium, calcium and copper ions.

$\ce{Li+}$ crimson/red; $\ce{Na+}$ yellow; $\ce{K+}$ lilac; $\ce{Ca^2+}$ orange-red; $\ce{Cu^2+}$ green/blue-green.

How are halide ions ($\ce{Cl-}$, $\ce{Br-}$, $\ce{I-}$) tested for and distinguished?

Add dilute nitric acid then silver nitrate solution: $\ce{Cl-}$ gives a white precipitate, $\ce{Br-}$ cream, $\ce{I-}$ yellow ($\ce{AgX}$ precipitate). $$\ce{Ag+ + Cl- -> AgCl(s)}$$

What gases make up today's atmosphere by approximate percentage?

Nitrogen about $78\%$, oxygen about $21\%$, argon about $0.9\%$, carbon dioxide about $0.04\%$, plus small amounts of other gases and water vapour.

Name three greenhouse gases and describe how the greenhouse effect causes warming.

Carbon dioxide ($\ce{CO2}$), methane ($\ce{CH4}$) and water vapour. They absorb outgoing infrared (long-wave) radiation from the Earth and re-emit it, trapping heat and warming the surface.