Unit 2: Thermodynamics and Rates of Reactions

Systems- Part of the universe that's being studied

Enthalpy - How much energy something has - AKA Heat content

Closed System - No Matter can move but energy can transfer between system and surroundings

Open System- Energy and Matter can Move between Surroundings and system

Isolated system - No matter and no energy can move between system and surroundings

Types of Enthalpies- Potential and Kinetic

Enthalpy Change- How much energy is absorbed or released from a system. (ΔH = q)

Thermochemical Equations show how much energy is absorbed or emitted in a chemical reaction

Exothermic: Energy is released from the system to the surroundings.
Endothermic: Energy is absorbed from the system to the surroundings.

Calculating Enthalpy Change

Bond Energy Method

  • Based on the energy of breaking and forming bonds

Calorimetry Method

  • Based off experimental results with enthalpy change
  • Reactions held in a Calorimeter
  • Assuming it's an isolated system, all aqueous solutions have the same heat capacity as water

Hess's Law

Additivity Method

  • identify step equations and put them with the list
  • Place them all together and balance all out to cancel all intermediates
  • Calculate Enthalpy change by adding all changes

Summation Method

  • Subtract the enthalpy change of the formation of products by the formation of reactants

Rates of a reaction - How fast a reaction occurs, measured by seeing how much reactant is being consumed over a period of time, can be measured through Volume, mass, color, pressure.

As time goes by, less product is produced over time, less reactant is consumed image

Reaction Mechanisms

To find the rate of the reaction you need to find the rate determining step AKA slow step AKA the step that requires most energy

Molecularity- Most common types of reactions occur with 1 or 2 reactants

Reaction Intermediates - Created in the steps but formed in the net equation

Maxwell-Boltzmann Distribution image
shows the number of molecules that have a certain energy, this means that reactions that require energy to begin could start. (Eg: Boiling water)

Collision Theory - A product of a reaction can only be created when the reactants hit each other in the correct way and with enough energy

Connection to Unit 5 Redox.
Finding Cell Potential (E) and Finding the enthalpy change (ΔH) require very similar steps such as stacking equations and reversing some to get a desired number

Connection to Unit 4 Equilibrium, you can see on the concentration time graph that the concentration of product and the concentration of reactant remain constant after reaching a point. That point is known as equilibrium

Connection to Unit 4: Equilibrium. If you apply heat to either of those reactions when the equilibrium would shift (Le Chatelier's Principle). If you apply energy to an Exothermic reaction the reaction would shift to the reactants, if you apply energy to an Endothermic reaction the reaction would shift to the products. This then shows that the Haber Process is an Exothermic reaction because taking energy away (Lowering temperature) Favors the products side.

Connection to Unit 3: Organic Chemistry. The substitution reaction in Organic Chemistry actually has many side products based on how the reactants collide. This actually shows the Collision theory in action as different orientations lead to different reactions and not always the same product (Propagation steps, Termination Steps)

Also Applies to endothermic Reactions, we need to add energy for the reaction to happen, which means there wasn't enough on it's own for the reaction to occur

Rate Law Expression: r = k(A)^a(B)^b