LAB 6 Flashcards
Thermochemistry
the study of the thermal energy changes that accompany chemical reactions
what are the energy changes called
heats of reaction
- can be observed by temperature changes under controlled conditions
exothermic
enthalpy of products is less than reactants and heat is produced
endothermic
q+ energy is absorbed from surroundings, enthalpy change will be positive
1 law of thermo
- at a constant pressure the change in molar enthalpy is equal to the heat evolved by the system in water during that change
Hsys=qpsys
qpsys=-qpsurr
calorimetry
amount of heat energy gained or lost in a chemical reaction
what will be the calorimeter in this experiment
insulated vessel
- designed to minimize heat transfer between the reaction vessel and atmosphere
transfer of heat energy
- leads to a change of temperature of the reaction vessels contents (surroundings)
temperature change associated with a change associated with a chemical reaction depends on what
the specific heat capacity
what is the specific heat capacity
amount of heat required to raise the temperature of 1g of the substance by 1 degrees celsius has units of J/g degrees celsius
delta H
enthalpy change when we convert from 100% starting materials to 100% products
- assumes reaction proceeds to completion
Hess’ Law
- enthalpy change for an overall reaction is independent of the reaction pathway
- therefore we can choose any pathway
- energy change is equal to sum of energy Changes
in the second part of the experiment we will use hess law to calculate what
the enthalpy of combustion of Mg
which reaction is too dangerous
and which is endothermic
- 6: dangerous so we will calculate from standard enthalpies
- 4: endothermic we can calculate by the negative of the reverse
what chemicals are dangerous in this experiment and what does hygroscopic mean
- NAOH and HCl
- NAOH is hygroscopic meaning it readily absorbs moisture from the air so close contained after use
