CHEM 103 LAB 4 THERMOCHEMISTRY (PORTAGE LEARNING)
Lab 4 Video Notes
Dr. Rodney Austin
Thermochemistry - all reactions result in some sort of heat change
● these heat changes are important in the lab as well as our everyday lives
● Consider all reactions that take place:
○ Combustion driving a car
○ Bodies give off heat in several reactions
○ Wood and coal to heat our houses and generate power
○ All of these are chemical based reactions where heat is given off
● Example: Methane reaction with oxygen to produce CO2 and Water
○ CH4 (g) + 2 O2 (g) → CO2 (g) + 2 H2O (l)△H = -212.8 KCal
○ Exothermic reaction because heat is given off
● In a thermochemical reaction, the heat change is added onto the reaction
○ Represented by Delta H (enthalPY) added on to the end of the reaction and gives us a heat value
○ The change in enthalPY is a negative 212 kiloCalories
○ Negative sign indicates that heat is given off
○ For every 1 mole of CH4 that burns, we get -212.8 Kilocalories of energy that is given off
○ If we double this, and go with 2 moles of CH4, effectively we would end up doubling this value
■ That would give us -405.6 kilocalories
■ Remember the negative (-) means giving off heat
○ Extensive Property of chemical reactions meaning it depends on the amount
■ Not all properties of reactions or substances are extensive; some properties are intensive
■ Example: density - the density of water is the same whether you have a few drops or a lot of it; the density
is ultimately the same (an intensive property)
● Reactions will give off heat in one direction and can pick up heat in another direction
○ CaCO3 → CaO + CO2 △H = +42.4 Kcal
● Calcium carbonate is heated and broken down as calcium oxide as well as CO2 being given off
● Delta H is + 42.4 kilo calories
○ The positive value of delta H means that it is an endothermic reaction because energy needs to be put in to make this
react
○ Positive means energy needs to go in to make the calcium carbonate break into calcium oxide and CO2 so they are
different
● However - in the reverse, if we take the same direction but write it in the opposite direction to produce calcium carbonate,
then we will have the same energy change but it will be the OPPOSITE sign because it is going in the opposite direction
○ The opposite would be exothermic because heat is given off
○ + sign means energy needs to be added to the direction (endothermic)
○ - sign means energy is given off (feels hot) which is exothermic)
● Chemical ice packs - break the components and it will cause a reaction of endothermic and it will feel cold
Now we will run 2 experiments to demonstrate chemical reactions
1) Acid base reaction
Acid-Base Reaction: thermochemistry
● We are going to experimentally determine what the heat of the reaction will be for delta H
NaOH + HCl → NaCl + H2O △H = ?
Salt water is being formed
What we will do:
● First we need to determine the weight (calorimeter)
This study source was downloaded by 100000841138256 from CourseHero.com on 05-29-2023 02:35:38 GMT -05:00
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