1.8 Thermodynamics

• Enthalpy change for the formation of one mole of a compound is formed from its elements in their standard states under standard conditions.
• Enthalpy change of solution is the change in energy when one mole of an ionic substance is dissolved in the minimum amount of solvent to ensure no further enthalpy change is observed upon further dilution.
• Enthalpy change of solution is calculated by knowing the lattice dissociation enthalpy and the enthalpy of hydration.
• An example of an enthalpy change for the formation of one mole of a compound is formed from its elements in their standard states under standard conditions is the formation of water.
• Enthalpy change for the formation of water is -239 kJ.
• The temperature change in the reaction between two solids is erratic and enthalpically unfavorable.
• The reaction starts with two solids but produces a gas and a liquid as product, leading to more disorder.
• Entropy change Delta s is the change in entropy between reactants and products, measured in joules per Kelvin per mole.
• Entropy values are given as a standard entropy, measured under standard conditions of one mole of substance, 100 kilo Pascal's of pressure, and a room temperature of 298 Kelvin.
• The temperature drop in the reaction between two solids is approximately a tenth at 20 degrees Celsius.
• The reaction is endothermic and has a value of plus one six four kilojoules per mole.
• The reaction is entropically favorable as it has more moles on the right than on the left.
• The reaction between M hydrated barium hydroxide and ammonium chloride results in the production of ammonia water and barium chloride.
• Born here is a bit like HESA cycles, with different routes to form lithium chloride.
• An alternative way to form lithium chloride is by forming ions in the gaseous state and then forming lithium chloride.
• The first ionization energy of lithium is the energy required to remove an electron to form lithium plus.
• One way to form lithium chloride is by elements in their standard states, forming a solid ionic lattice which is lithium chloride.
• To form ions in the gaseous state, we need to break the bond between chlorine atoms and form a single chlorine acid.
• The enthalpy of atomization of chlorine is the energy required to break the bond between chlorine atoms and form a single chlorine acid.
• The next step is to convert lithium solid into lithium gas.
• The electron affinity is the energy required to add an electron to chlorine, which is an exothermic process because chlorine needs one more electron to complete a full shell with seven electrons valence electrons.
• The first electron affinity is exothermic because it involves adding an electron to a neutral atom and forming a negatively charged ion.
• The second electron affinity is endothermic because it involves adding an electron to an ion that is already negatively charged.
• The next step in the cycle involves forming magnesium oxide by adding an electron to magnesium 2+ and oxygen 2- ions.
• Lattice enthalpy is calculated by subtracting the start point from the end point.
• The direction of the reaction is determined by the arrow on the chemical equation.
• The reason why the second electron affinity is endothermic is because of repulsive forces between a negative electron and a negative ion.
• The start and end points are determined by the direction of the reaction.
• The answer should be positive if the reaction is endothermic and negative if the reaction is exothermic.
• The decomposition of sodium hydrogen carbonate is an endothermic process that is not a favorable process, but it does occur from a solid to a gas.
• Exothermic reactions with a positive entropy will always be feasible, regardless of the temperature.
• Freezing water is an exothermic process that gives out heat energy when we freeze water, and it only happens below a certain temperature.
• If Delta G is 0, the reaction is not feasible.
• Endothermic reactions with a negative entropy will never be feasible, regardless of the temperature.
• If Delta H is negative and Delta s is positive, the reaction is not feasible.
• If Delta H is negative and Delta s is negative, the reaction is feasible at any temperature.
• Reaction feasibility can be calculated by subtracting a larger number from the enthalpy (ΔH) and entropy (Δs) parts of the reaction equation.
• If Delta H is positive and Delta s is negative, the reaction is not feasible.
• The number of particles and the arrangement of particles both affect change in entropy.
• Gases have the greatest amount of disorder, with particles spaced out the most and having the most freedom to move around.