Unit 3 (chapter 5) Flashcards
Thermochemistry
The study of the energy changes that accompany chemical, physical or nuclear changes in matter
Energy
The capacity to do work (joules)
Kinetic energy
Energy due to motion of an object, vibration of atoms
Rotation of translation of molecules within a substance
Potential energy
Energy due to position, elecytic potential energy of atoms connected by bonds
Thermal energy
A form of kinetic energy that results from the motion of particles
Heat
The transfer of thermal energy to a warmer to a cooler object
Temperature
The average kinetic energy possessed by a molecule within a substance
Chemical system
A group of reactants and products
Surroundings
All the matter around the system that is capable of absorbing or releasing energy
Open system
A system where both matter and energy are free to both enter and leave the system
Closed system
Energy can enter and leave the system but matter cannot ex. closed jar of boiling water
Isolated system
An ideal system which neither matter or energy can move in or out
Endothermic
Absorbing energy from the surroundings in order to create products +delta H
Exothermic
Releasing energy to the surroundings - delta H
Calorimetry
Process of measuring energy changes in a chemical system
Enthalpy change
The energy absorbed or released to the surroundings when a specific chemical change occurs in a chemical system
Molar enthalpy
The energy change associated with one mole of a substance undergoing a specific change
Hsol
Solution
Hvap
Vaporization
Hfr
Freezing
Hneut
Neutralization
Hf
firmation
Hsys
= n (deltaHx) or q/n
Assumption for calorimeters
- No heat is transferred to the outside environment
- Any heat absorbed by the calorimeter is negligible
- A dilute (aq) solution is assumed to have the same density and specific heat capacity as water (c=4.18J/gc)
Hx
molar enthapy
Thermochemical equation
Add number in chemical equation (Left side= endothermic, right side= exothermic)
Chemical equation and starting H
H is off to the side
Stating molar enthalpy of the reaction
Hdecomp= 285 kJ/mol H2O
Chemical potential energy diagram
y= ep(kj)
x= rxn progress
Hess’s law
1) If a chemical equation is reversed the sign of delta H changes
2) If the coefficients of a chemical system are altered by multiplying of diving by a constant factor, then the delta H is altered the same way
3) Formulas cancelled from both sides of an equation much be for the same substance in the same state
Enthalpy change without using hess’s law
Sum of products- sum of reactants
