Chapter 6 Definitions Flashcards
Thermodynamics
The general study of energy and its conversions
Kinetic Energy
Energy associated with motion
Thermal Energy
Energy associated with temperature
Energy
The ability to do work
Work
Force acting through a distance
Heat
The flow of energy caused by temperature difference
Potential Energy
Energy associated with positions or composition
Chemical Energy
A form of potential energy associated with positions of electrons and nuclei in a system
Thermochemistry
The study of heat energy associated with chemical reactions and physical transformations
What is the Law of Conservation of Energy
Energy can neither be created nor destroyed, but it can be transferred from one object or system to another.
System
A specific area of interest
Surroundings
Everything else (i.e. the universe)
First Law of Thermodynamics
The total energy of the universe is constant
Internal energy (U)
The sum of the kinetic energy and potential energies of all of the particles in a system
The state of the system is defined by parameters like:
Temperature, Pressure, Concentration, and Physical State
Summarize Energy Flow for reactants with higher internal energy
If reactants have higher internal energy than the products, the ‘triangle’Usys is negative and energy flows out of the system into the surroundings. The surroundings is negative and energy is decreasing.
Summarize Energy Flow for reactants with lower internal energy
If reactants have lower internal energy than the products, the ‘triangle’Usys is positive and energy flows into the system from the surroundings. The surroundings is positive and energy is increasing.
Heat Capacity (C) of a system
The quantity of heat required to change its temperature by 1degreesC or 1K. Depends on mass
Two types of calorimeters (Heat of reactions are measured in calorimeters)
Bomb Calorimeters: Constant Volume
Coffee Cup Calorimeters: Constant Pressure
Two types of Heat Capacity
Specific Heat Capacity: Heat Capacity per gram of a material (does not depend on mass)
Molar Heat Capacity: Heat Capacity per mole of a material (depends on mass)
Pressure-Volume Work
The force is caused by a volume change against an external pressure
Heat is proportional/disproportional to temperature
Proportional
List the state function.
Internal Energy (U), Pressure(P), Volume(V), and H(enthalpy). Its’ value depends only on the state of the system
Heat and work are not path functions. True/False
False. Path functions depend on the path taken to reach one state from another
Closed System
Pressure changes, and volume remains constant
Open System
Volume remains constant, and pressure changes
Enthalpy
The heat evolved in a chemical reaction at constant pressure
If enthalpy is greater than 0. What is the reaction?
The reaction is endothermic
If enthalpy is less than 0. What is the reaction?
The reaction is exothermic (it releases energy)
Exothermic Reactions
Negative Enthalpy - Gives off heat heat from the surroundings
Weaker bonds break and stronger
bonds form
* Electrons reorganize
* Molecules reorganize
* Potential energy converts to thermal
energy
* Reaction gives off thermal energy
* System is more stable, lower in
potential energy
Endothermic
Positive Enthalpy - Absorbs heat from the surroundings
Weaker bonds forms and stronger bonds break
* Electrons do not reorganize
* Molecules do not reorganize
* Potential energy converts to thermal
energy ???
* Reaction do not give off thermal energy
* System is unstable, higher in
potential energy
Hess’s Law
The enthalpy changes of the reaction carried out in multiple steps is equal to the sum of the enthalpy changes for each individual step.
