Thermochemistry. Chapter 5 Regular Chem book = Ch 11. Hmmmmmm …. When we eat calories where is the HEAT in food? What do we do with it (what do we convert it into) when we “burn” calories?. Food’s heat is in its bonds- it’s energy is being used to hold the particles together
Regular Chem book = Ch 11
Mg + HCl MgCl2 + H2
But, that’s only part of the story because this reaction gives off lots of heat!
That turns a chemical equation into a thermochemical equation
There are 3 different ways to write a thermo equation:
1 mole of ice needs to absorb 285kJ of heat in order to melt. Write the thermo equation 3 ways.
The combustion of methane releases 890kJ of heat. Write the equation for this reaction 3 ways.
Wait, combustion releases heat but you have to add heat to make it happen. What’s up with that?
Interesting little tidbit… this is the reaction when you make cement. You add little rocks and stuff to CaO and then add water.
CaO + H2O Ca(OH)2 + 65.2kJ
Which means that 1 mole of CaO produces 65.2kJ of heat
…and that adds another arrow to the molar conversion map
4 x 65.2 = 260.8 kJ
100/56 x 65.2 = 116.4 kJ
1000/65.2 x 56 = 858.9g
Fe2O3 + 3CO 2Fe + 3CO2 + 26.3kJ
1.2/3 x 26.3 = 78.9
100 / 22.4 / 3 x 26.3 = 39.1kJ
So… you’re out walking barefoot on a 90o day and you have the choice to step on
(a) the sidewalk
(b) a manhole cover
(c) a puddle
What would you do?
(Specific) Heat capacity = the amount of heat it takes to raise 1g of a substance by 1oC
-- Water is high, metal is low
-- What else is high & low? (p. 296)
-- What’s up with the oranges on p. 297?
q = mCΔT
q is the heat in cal or J
m is the mass in g
C is the specific heat in J/goC or cal/goC
ΔT is the temp change in oC
Try #1-3, 8-10 on page 299
94.6g of Cu heats up 2540oC by absorbing 849J, what’s its specific heat?
100g of an unknown metal cools 6020oC by absorbing 132 cal of heat. What metal is it?
0.03 J/goC, Mercury