Thermochem Flashcards
(17 cards)
What is Thermochemistry?
Study of energy changes that accompany physical or chemical changes in matter
Thermal Energy
Energy available from a substance as a result of the motion of its molecules
Chemical System
a set of reactants and products under study, usually represented by chemical equation
Surrounding
All matter around the system capable of absorbing or releasing thermal energy
Heat
amount of energy transfered between substances
q= mc T (change of temp)
Exothermic
releasing thermal energy as heat flows out of system
Endothermic
absorbing thermal energy as heat flows out of the system
Temperature
average kinetic energy of particles in a sample of matter
Open System
Both matter and energy can move in or out
Isolated system
Ideal system - neither mutter nor energy can more in or out
Closed System
Energy can move in or out, but matter cannot
Calorimetry. What do we assume about this?
- Technological process of measuring energy changes in a chemical system
Assume:
- no significant amount of gas produced
- no heat transferred from calorimeter to outside environment
- any heat absorbed or released by calorimeter is negligible
- dilute solutions have density and specific heat capacity of pure water (1.00 g/mL and 4.18 J/g C)
Specific Heat Capacity
Quantity of heat required to raise temperature of a unit mass
Hess’s Law
heat evolved or absorbed in a chemical process is the same whether the process takes place in one step or several steps
Standard Enthalpies of Formation
the enthalpy change for the reaction that forms 1 mole of compound from its elements with all substances in their standand state
Hess’s Law of Summation
enthalpy change of chemical rxn is calculated by adding the heat of formation of the products subtracted by the heat of formation of the reactants
Additional
- If you reverse an equation the ∆H must switch signs.
- If you need to multiply or divide any part of the
equation, the whole equation must follow the same
operation, including ∆H.
4 ways to express thermochemical equations
1) as an equation
2) as change of H value
3) as molar enthalpy
4) as a potential energy diagram
