Chapter 5 Thermochemistry Flashcards
Thermodynamics
Study energy and its transformations
Sytem
part of the universe of interest (reaction vessel)
Surroundings
rest of the universe
3 Types of Systems
Open, Closed, and Isolated
Open System
Mass, heat, energy can be exchanged
Closed System
No mass exchanged-only heat, energy, and work
Isolated System
No mass, heat, or work can be exchanged (ex: universe)
Where does the exchange take place?
At boundary btw system and surrounding during a change in state
State
Condition in which all variables are fixed and unvarying
When does a system change its state?
When one or more of these variables are changed (Temp, Gas at V1, P1, T1–>Gas at V2, P2, T2, Phase change-solid to gas/gas to solid
Isothermal Change
Change at constant temp (supply or take away heat to maintain temp)
Abiabatic Change
No heat exchanged during change-system is insulated from surroundings
Isobaric Change
One at constant pressure
What are normal laboratory conditions?
Isothermal and Isobaric
Thermochemistry
Study of relationships btw chemical reactions and energy changes
Energy
Capacity to do work or transfer heat
Work
energy used to cause an object to move against a force
Heat
energy used to cause objects temperature to increase
Two types of energy
Kinetic and Potential
Kinetic Energy
energy of motion-dependent on mass and velocity/speed
Potential Energy
stored energy-stored btw bonds of molecules (potential energy is transferred to kinetic energy)
Electrostatic Potential Energy
energy that comes from interaction of charged particles
Units of Energy
Joule (J) and Calorie (cal)
1 cal = ? J
4.184 J
Cal
Calorie of food
cal
calorie of energy
1st Law of Thermodynamics
energy is conserved-neither created nor destroyed
Endothermic
absorbs energy from surroundings (ex. ice melting)
Exothermic
system gives off heat to surroundings (ex. combustion reaction)
State Functions
property of a system-determined by specifying systems condition of state
Enthalpies of Reactions (H)
Heat of RxN= Hproducts - Hreactants
Hess’s Law
If RxN carries out in a series of steps, H = sum of enthalpy changes for individual steps
Enthalpies of Formation
enthalpy change associated with formation of a cmpd from its elements (depends on state)
Standard Enthalpy Change
enthalpy change when all reactants and products are in their standard states (1 atm and 25 degrees celsius)
