Chapters 11 & 12
Enthalpy Change
Explaining Chemical Changes
Energy Sources
Calorimetry
Calorimeters
Isolated systems are systems where neither matter nor energy can be transferred between itself and its environment. This is necessary in calorimetry to determine precise quantities of transferred energy.
Thermal Energy
Specific heat capacities
Enthalpy refers to the total amount of energy in a system.
Calculates the amount of thermal energy transferred in Joules or kiloJoules
Formula: Q = mcΔt
Where: Q is the quantity of thermal energy transferred
m is the mass of the substance
c is the specific heat capacity of the substance
and Δt is the change in temperatur
Communicating Enthalpy CHanges
Molar Enthalpy
Enthalpy Change
Term in a Balanced Equation
Endothermic: heat/energy is a reactant Exothermic: heat/energy is a product
Chemical Potential Energy Diagram
Hess's Law
Bond Energy
Catalysis
Activation Energy
Activation energy is the energy required for a chemical reaction to occur (heat, light, electricity)
Collision-Reaction Theory states that 4 things are necessary for reactions to occur between particles: Collision, Orientation, Movement, and Energy
Catalysts are substances that increase the rate of reaction without being consumed in the overall process
Catalysts provide an alternative pathway that requires less activation energy
Does not affect net enthalpy of a reaction
Enzymes are organic molecules (usually proteins) that catalyze biological reactions
Reaction Progress
Intermediates are entities formed at an in-between stage of a reaction. They are less stable than the product, and do not appear in the final product.
Activated Complexes are molecules formed from the collision of the reactants before becoming the products
A specific heat capacity is the amount of energy needed to change the temperature of 1 gram of a substance by 1 degrees Celcius.
The specific heat capacity of water (it is also used as a constant for substances with no determined specific heat capacity) is 4.19 J per g°C
All chemically stored energy originates from the Sun, energy can come from photosynthesis in plants which use the Sun's electromagnetic energy.
Molar enthalpy describes the energy needed for 1 mole of a given substance to react in a certain way, whether formation, combustion, etc.
Molar enthalpy of oxidation of ammonia (ΔoHm) is -905.2kJ / 4 = -226.3 kJ/ mol NH4
4NH₃(g) + 5O₂(g) → 4NO(g) + 6H₂O(g) + 905.2 kJ.
4NH₃(g) + 5O₂(g) → 4NO(g) + 6H₂O(g) ΔH = -905.2 kJ
Negative value is exothermic, positive value is endothermic
High-Low, Exo!
Endothermic: positive 'slope' Exothermic: negative 'slope'
The total enthalpy change for an equation is the sum of all changes.
Smaller equations that appear in a larger equation can be used to determine the enthalpy of a more complex equation.
ΔrH= ΔH1 + ΔH2 + ΔH3....
We can use this easier equation to do the same thing:
ΔH°rxn = Σ ΔH°f, products minus Σ ΔH°f, reactants
Photosynthesis (endothermic)
6 CO2 + 6 H2O → C6H12O6 + 6 O2
Cellular Respiration (exothermic)
C6H12O6 + 6 O2 → 6 CO2 + 6 H2O
Calorimetry examples & bomb calorimetry http://www.physicsclassroom.com/class/thermalP/Lesson-2/Calorimeters-and-Calorimetry
Reference molar enthalpy: enthalpy of equation set at zero to compare other reactions
Activation energy graph https://www.quora.com/What-is-the-activation-energy-chemistry
It requires energy to break bonds, forming bonds produces energy.
bonded particles + energy = separated particles
separated particles = bonded particles + energy