Lecture 2 Flashcards
What is internal energy?
The SUM of the KINETIC and POTENTIAL energies of all the particles in the system.
Equation for the change in the system’s internal energy:
ΔE= q + w
What is the third law of thermodynamics?
ENTROPY is temperature DEPENDENT. If all the thermal motion of all molecules (kinetic energy) could be removed, a state called ABSOLUTE ZERO would occur.
What is absolute zero?
0 KELVIN = -273.15° CELSIUS
What is thermochemistry?
The study of energy changes accompanying a chemical reaction, so the AMOUNT of energy taken in or given out.
What is enthalpy?
ENTHALPY is a measure of the amount of heat RELEASED or CONSUMED by a reaction..
Thermodynamic Definition of Enthalpy:
H = E + PV E = Energy of the system & P = pressure of the system & V = volume of the system
When heat is released during a reaction what happens to ΔH and the relative stability of bonds?
Products > Reactants
ΔH < 0
When heat is consumed during a reaction what happens to ΔH and the relative stability of bonds?
Reactants > Products
ΔH > 0
When there is no heat change during a reaction what happens to ΔH and the relative stability of bonds?
Reactants = Products ΔH = 0
What is the standard enthalpy of formation?
STANDARD ENTHALPY OF FORMATION is the change in enthalpy that accompanies the formation of one mole of a COMPOUND from its ELEMENTS with all substances in their standard STATES.
What is the symbol for the standard enthalpy of formation?
∆Hfө.
What is the standard enthalpy of formation of a PURE ELEMENT in its standard state is defined as?
Zero
What does a bomb calorimeter study?
How does it do this?
Exothermic Reactions
Heat energy is transferred to raise the temperature of its surroundings (water).
What is the Enthalpy Change equation for Calorimetry?
∆H = mCp∆T
What does Hess’ Law state?
“The overall enthalpy change accompanying a chemical reaction is INDEPENDENT of the route taken in going from reactants to products.”
When does Hess’ law only apply?
Same initial and final states of TEMPERATURE and PRESSURE are applied to the REACTANTS and PRODUCTS.
Enthalpy Change equation Hess’ Law:
∆H = ΣHproducts - ΣHreactants
How can the ∆H for a reaction can be calculated?
Heat of FORMATION of ALL REACTANTS and PRODUCTS (Hess’s Law).
BOND ENERGIES of INDIVIDUAL BONDS.
Calorimetry
How do you calculate enthalpy changes using Hess’ law cycle?
- Question- Equation
- Balance it!
- Information in Question to Construct Cycle.
- Arrows
- Answer
What is the equation to workout HR (Bond Energies)?
HR = ΣHbroken +ΣHformed
