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Chem
Energy
| Question | Answer |
|---|---|
| Standard lattice enthalpy | Enthalpy change that accompanies the formation of an ionic compound from its gaseous ions under standard conditions |
| Born-Haber cycles | Enthalpy of formation = Enthalpy of atomisation + Ionisation energy + Electron affinity + Lattice enthalpy |
| First ionisation energy | Enthalpy change required to remove 1 electron from each atom in 1 mole of gaseous atoms to form 1 mole of gaseous 1+ ions under standard conditions |
| Standard enthalpy change of formation | Enthalpy change that takes place when 1 mole of a compound is formed from its elements under standard conditions |
| The steps of dissolving | 1. Ionic lattice is broken (negative lattice enthalpy) 2. Water molecules are attracted to and surrounds the ions (hydration) |
| Standard enthalpy change of solution | Enthalpy change that takes place when 1 mole of a solute dissolved in a solvent in standard conditions |
| Standard enthalpy change of hydration | Enthalpy change that accompanies the dissolving of gaseous ions in water to form 1 mole of aqueous ions in standard conditions |
| Enthalpy cycles with enthalpy of solutions | Enthalpy of solution = Negative lattice enthalpy + enthalpy of hydration |
| Factors affecting lattice enthalpy | Ionic radius: Larger radius - weaker attraction between ions - lattice energy less negative - lower melting point Ionic Charger: Larger charge - stronger attraction between ions - lattice energy more negative - greater melting point |
| Factors affecting enthalpy change of hydration | Ionic radius: Larger radius - weaker attraction between ions and water molecules - hydration energy less negative Ionic charger: Larger charge - stronger attraction between ions and water molecules - hydration energy more negative |
| Entropy | A measure of the dispersal of energy in a system - greater entropy = more disordered |
| Entropy increases when... | State change from solid to liquid to gas There are more gaseous molecules in the products of a reaction |
| Standard entropy of a reaction calculation | Sum of the standard entropy of the products - Sum of the standard entropy of the reactants |
| Feasibility | Whether a reaction is able to occur energetically |
| Free energy and the Gibbs' equation | ΔG = ΔH - TΔS Free energy is the overall change in energy in a chemical reaction Feasible when ΔG < 0 Can be graphed and translated as y = mx + c where y = ΔG, x = T, c = ΔH, m = -ΔS |
| Predicting feasibility | ΔH+, ΔS- = not feasible ΔH-, ΔS+ = feasible ΔH+, ΔS+ = feasible at high temp ΔH-, ΔS- = feasible at low temp |
| Limitations of predictions of ΔG | Only accounts for thermodynamic feasibility not kinetics/rate of reaction |
| Oxidising and reducing agents | Oxidising - takes electrons away, gets reduced Reducing - gives away electrons, gets oxidised |
| Fe2+/MnO4- titration | KMnO4 in burette, Fe solution in conical flask with excess dilute H2SO4 for H+, no indicator as it is self indicating MnO4- reduced, Fe2+ oxidised End point at first permanent pink colour, read from top of meniscus as KMnO4 is too dark |
| I2/S2O3^2- titration | Na2S2O3 in burette, oxidising agent + KI in conical flask forming I- making the solution yellow S2O3^2 oxidised, I2 reduced When solution is straw coloured, starch is added making the solution blue/black due to I-, end point when blue/black disappears |
| Standard electrode potential | The e.m.f of a half cell connected to a standard hydrogen half cell under standard conditions |
| Half cells | Each cell contains a solution of ion(s) and a corresponding metal electrode or platinum if multiple ions are in the solution - electrodes connected by a voltmeter, solutions connected by a salt bridge of an unreactive solution |
| Standard cell potential | Positive electrode potential - Negative electrode potential |
| Reading electrode potentials | More negative - more likely to be oxidised Less negative - more likely to be reduced Electrode potential data shows forward reaction as reduction |
| Limitations of predictions using standard cell potentials | Don't account for rate of reaction/activation energy Standard potentials use 1moldm3, different conc affects equilibrium and thus the negativity of the cell potential Conditions may not be standard Only applies to aqueous equilibria |
| Fuel cell | Uses the energy from the reaction with oxygen to create a voltage |
Created by:
silver54331