Ch 5 Terms Flashcards
Hess Law
Indirect determination of OH; if you add several reactions together to get an overall reaction, you can also add their 🔺 H together
Energy
Transfer of heat
Thermochemistry
Study of heat absorbed or released in reactions
Chemical potential energy
Energy stored in chemical bonds
*Energy is required to to break ANY BOND
Heat (q)
Energy needed to increase an objects temperature
System
What we’re studying
Always the REACTION
Surroundings
Everything else
Ex: water, beaker, thermometer, you
If heat is lost by system, the surroundings gain it and vice versa
Exothermic
Heart is being released by system
The surroundings gain heat
You feel warmth
All combustions
q system= -
When discussing heat, we take the ___ perspective
Systems
Endothermic
Heat is absorbed by the system
Surroundings lost heat
You feel cold
q system = +
Joule to calorie conversion
1 calorie = 4.18 J
Heat capacity
Amount of heat needed to raise the temp of a substance by 1 degree Celsius
Depends on:
1. Substance density
2. Mass
Specific heat (c)
Amount of heat needed to raise one gram of substance by 1 degree Celsius
Enthalpy
Another term for heat (at constant pressure)
Heat = Enthalpy
Enthalpy changes depend on ____
Reaction conditions
Scientists pick a standard state
25 c and 1 atm (pressure at sea level)
Standard heat of formation
Heat absorbed or released when 1 mol of a substance is formed from its elements in their standard state
Calorimetry
A lab technique to determine q for 🔺H for a reaction
Calorimeter
An insulate device used to hold a reaction
Ex: styrofoam cup
“Coffee cup calorimetry”
Enthalpy is an extensive property
Heat depends on stoich
Big Bonfire = more heat
The enthalpy change for a reaction is equal in magnitude, but opposite in sign to H for the reverse reaction
The enthalpy change for a reaction depends on the state of the
Reactants and products
Thermochemical equation
Reaction with an H value
Constant pressure calorimetry
all reactions we study will occur in a coffee cup open to air (atmosphere pressure)
Solid to Gas
Sublimation (dry ice) (endo)
During a phase change
Temp does not change
Gas to Solid
Deposition (exo)
Liquid to solid
Freezing or solidification (exo)
Gas to liquid
Condensation (exo)
Solid to liquid
Melting/fusion (endo)
Liquid to gas
Vaporization/evaporation (endo)
Molar heat of fusion
Energy needed to melt 1 mol of substance (6.01 kj/mol)
Molar heat of solidification
Energy released when 1 mol of a substance freezes (-6.01 kj/mol)
Molar heat of vaporization
Energy needed to vaporize 1 mol of a substance (40.7 kj/mol)
Molar heat of condensation
Energy released when 1 mol condenses (-40.7 kj/mol)
Molar heat of condensation
Energy released when 1 mol condenses (-40.7 kj/mol)
Going up every q must be positive
Going down every q must be negative
Going up every q must be positive
Going down every q must be negative
