Unit 3: Energy Changes and Rates of Reactions Flashcards
(34 cards)
Chemical Kinetics
The area of chemistry that deals with rates of reactions
Rate of reaction/reaction rate is obtained by…
Measuring
Whats the average reaction rate equation?
r = △C/ △t
Simple Reactions
Take place in one elementary step (bimolecular)
Complex Reactions
- Take place in a series of steps (mechanism) which adds up to the same net equation
- Each step has its own activation energy that must be reached. Complex reaction mechanisms contain reaction intermediatics
- These are products of one reaction that immediately become reactions in another reaction
- Reaction intermediates do not appear in the net reactions
Thermochemistry
The study of the energy changes that accompany physical or chemical changes in matter
Physical Change + Example
Change in the arrangement of the molecules
Example: Hydrogen boils at -252 degrees
Chemical Change+ Example
Change in electronic structure
Example: Hydrogen is burned as fuel in space shuttles
Nuclear Change+ Example
Change in the nuclei of the atoms
Example: Hydrogen undergoes nuclear fusion in the sun producing helium
Exothermic (-)
Energy leaves the system
Endothermic (+)
Energy enters the system
Open System
Matter and energy can move in/out of the system
Example: Burning marshmallow
Closed System
Energy can move in/out but not matter
Example: Styrofoam cup
Isolated System
Ideal system; Neither matter or energy can move in/out
Example: Bomb Calorimeter
Calorimetry
The technological process of measuring energy changes in a chemical system
What are the 3 factors that are combined in an equation to represent the quantity of heat (q) transferred?
1) Mass
2) Type of substance (c); specific heat capacity
3) Temperature Change △T
What are the two equations for calculating energy changes?
1) q=mc △T
2) △T= T2-T1
Specific Heat Capacity
The quantity of heat required to raise the temperature of a unit mass of a substance by one degree
Enthalpy Change (△H)
The difference in enthalpies of reactions and products during a change
Law of Conservation of Energy
The total energy change of the chemical system is equal to the total energy change of the surroundings
What are the 3 types of enthalpy change?
1) Physical Change
2) Chemical Changes
3) Nuclear Changes
Molar Enthalpy (△Hx)
The enthalpy change associated with a physical, chemical, or nuclear change involving one mole of a substance (kJ/mol)
What is the equation used to find molar enthalpy?
△H= n△H
What are the 3 assumptions made when using calorimetry?
1) no heat is transferred between the calorimeter and the outside environment
2) Any heat absorbed or released by the calorimeter materials is negligible
3) Dilute aqueous solutions are assumed to have a density and specific heat capacity equal to that of pure water
