warm-up mg(s) + hcl(aq) h 2 (g) + mgcl 2 (aq) how much h 2 (g) is produced (in grams) in the above...
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Warm-up
Mg(s) + HCl(aq) H2(g) + MgCl2(aq)
How much H2(g) is produced (in grams) in the above reaction if we have a mass of 0.9 grams Mg and 1.87 grams of HCl?
Mg = 24.31g/mol
H = 1.01g/mol
Cl = 35.45g/mol
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ObjectiveSWBAT calculate energy changes
in a thermodynamics problem set
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Chemical Chemical ThermodynamicsThermodynamicsStandard 7
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Specific Heat Specific Heat 7d7dThe specific heat of a
substance is the amount of energy needed to change the temperature of 1gram by 1˚C.◦Every substance has its own specific
heat.Specific Heats of Common Substances
Substance Specific Heat (J/g˚C)
Water (l) 4.184
Ethanol (l) 2.44
Aluminum (s) 0.897
Silver (s) 0.235
Gold (s) 0.129
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Logical Thinking (don’t Logical Thinking (don’t write)write)Since it takes 4.184 Joules to
raise the temp of 1gram of water 1˚C, how much would it take to:
◦Raise 2 grams 1˚C?
◦Raise 1 gram 2˚C?
◦Raise 2 grams 2˚C?
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Heat added here doesn’t change the temperature of the substance, it is causing the phase change.
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Heat Flow ProblemsHeat Flow ProblemsTo calculate heat, use the following
formula:
◦Energy = mass * specific heat * temperature change
Always given to you!
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Practice ProblemsPractice ProblemsIf 200.0 grams of water is heated
from 70.0° C to 100.0° C to make a cup of tea, how much heat must be added?
Q = (m)(c)(ΔT) )0.700.100)(184.4)(0.200( CCg
JgQ
25100Q Joules
Calculations:
4.184J/gC
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Latent HeatLatent Heat 7d cont7d contLatent (hidden) heat is energy
added to a substance that doesn’t change the temperature.◦Instead, it is used to change the
phase solid liquid liquid gas
What is latent heat and what is it used for?
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Energy Requirements for the Changes of State Changes of state
are physical changes ◦No chemical bonds
are broken
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Energy Requirements for the Changes of State
Molar heat of fusion – energy required to melt 1 mol of a substance
• Molar heat of vaporization – energy required to change 1 mol of a liquid to its vapor
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Practice ProblemsPractice ProblemsIf 200.0 grams of water is at
100.0° C, how much heat must be added to change it all to steam or gas?
Hvap = 40.6 kj/molkJ
OmolH
kj
OgH
OmolHgQ 451)
1
6.40)(
02.18
1)(0.200(
22
2
JxJkJQ 51051.4451000451
Calculations:
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Putting it all togetherPutting it all togetherIf 200.0 grams of water is heated
from 70° C to 100.0° C and then a complete phase change is made to steam, how much energy was required?
kJkJkJQ 476)2(#451)1(#1.25
Calculations:
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SummarySummaryWhat is temperatureWhat happens when you heat a substance?Describe endo/exothermic reactions.What is ΔH for endo/exothermic reactions?Where does the energy go during phase
changes?Be able to calculate heat problems.What is latent heat used for?