A safe carbon store
Carbon dioxide dissolves in water via the following reactions:
CO2 (g) <==> CO2 (aq)
CO2 (aq) + H2O (l) <==> H+ (aq) + HCO3- (aq)
HCO3- (aq) + H2O (l) + CO3 2- (aq)
Adding these togther gives the overall equation:
CO2 (g) + H2O (l) <==> 2H+ (aq) + CO3 2- (aq)
As human activity increases atmospheric carbon dioxide a range of methods, such as more economical use of Carbon dioxide, and increased levels of photosynthesis, have been suggested to improve the situation.
Energy, entropy and equilibrium
The entropy change, equations
The entropy change for a chemical system is the is the difference between the entropies of the reactants and products in the equation for the reaction:
ΔS(system) = ∑ΔS (products) - ∑ΔS (reactants)
The entropy change for the surroundings depends on the transfer of heat to/from the surroundings.
ΔS(surroundings) = ΔH / T
ΔS (total) = ΔS(surroundings) + ΔS(system)
Knowing the total entropy change enables predictions to be made.
- if ΔS (total) is positive, a reaction will occur spontaneously
- if ΔS (total) is 0, the reaction is at equilibrium.
Energy changes and solutions
When ionic compounds dissolve in water, the ionic lattice is broken up and the ions separate and become hydrated. Energy is used to break up the lattice (ionic bonds are broken) but energy is given out when the ions are hydrated (ion-dipole bonds are formed)