Section 3: Thermodynamics, or why do things happen the way they do?
Balanced chemical reactions are the math of chemistry
- They show the relationship between the reactants and the products
How will chemical reactions proceed?
- Thermodynamics allows us to calculate the feasibility of reactions and to understand when/how equilibrium is established
Equilibrium
- Allows us to understand chemical processes such as ionic speciation, oxidation state distributions gas solubility, the carbonate system
Balancing equations, oxidation state, redox
Equation balancing:
Examples: If a solution of lead nitrate is added to a solution of sodium chloride, lead chloride precipitates:
Conventional equation:
\[\ce{Pb(NO_3)_{2(aq)} + 2NaCl_{(aq)} <=> PbCl_2(s) + 2 NaNO_{3(aq)}}\]
An ionic equation is written to show the actual species in solution:
\[Pb_2^+_(aq) + 2 NO_3^-_(aq) + 2 Na^+_(aq) + 2 Cl^-_{(aq)} <=> PbCl_2_{(s)} + 2 Na^+_{(aq)} + 2 NO3^-_(aq)\]
This equation contains spectators that are not interacting, we can eliminate those spectators to get a net ionic equation:
$\ce{Pb2+(aq) + 2 Cl-(aq) –> PbCl2(s)}
Steps in writing a net ionic equation:
- Write the conventional equation, including designations of state [(g), (l), (s), (aq)]. Balance the equation.
- Write the ionic equation by replacing each dissolved substance (aq) with the species in solution. Never change states in this step. Be sure the equation is balanced for both atoms and charge.
- Write the net ionic equation by removing the spectators. Reduce coefficients to lowest terms. Be sure the equation is balanced for both atoms and charge.