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Thermochemistry

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Brett McMillan

on 15 May 2013

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Transcript of Thermochemistry

435 J + 3.4 g Olive Oil; T 25ºC 85ºC
So...what is C of Olive Oil? Heat Thermochemistry Some say the world will end in fire,
Some say in ice.
From what I’ve tasted of desire
I hold with those who favor fire.
But if it had to perish twice,
I think I know enough of hate
To say that for destruction ice
Is also great
And would suffice. "Fire and Ice" Energy Transformations Exothermic and Endothermic Processes Heat Capacity Specific Heat Energy Flow Calorimetry Thermochemical Equations Heat of Reaction Heat of Combustion Enthalpy
The capacity to do change
can only be measured indirectly based on the changes it causes
energy is related to or made of both work and heat
two main kinds of energy
??? Chemical Kinetic Potential A B D C
Study of Energy Changes V: Thermochemistry V: Energy physical: phase changes chemical: reactions V: chemical potential energy energy stored in chemical bonds of a substance
EX:when an ionic compound dissociates in water, heat is absorbed or released
In order to determine the heat lost or gained the following formula can be used: q = m C T Breaking Bonds
Making Bonds absorbs energy
releases energy WHY?: GLUCOSE (6-C sugar) MW ~180 HEXANOIC ACID (6-C fatty acid) MW ~116 Note: CAPRIC ACID (10-C fatty acid) MW ~172 19 C-H Bonds V: energy that transfers from one object/substance to another because of a temperature gradient q symbol for heat in equations...
signs make a difference!
-q=energy leaving
+q=energy being absorbed UNITS: HEAT (and other kinds of energy) can be measured in..
calories c based on energy as heat [1gm or 1ml water 1ºC]
kcals C (not centigrade) [1 L or 1kg water 1ºC]
joules J based on energy as work (1 N m) 1J = 0.2390 cal
1 cal = 4.184 J (~1/4)
(~4) Exothermic and Endothermic
Processes Exothermic Endothermic -a change (e.g. a chemical reaction) that releases heat.
-Exothermic process: -q
-Temperature of surroundings Rises -a change (e.g. a chemical reaction) that requires (or absorbs) heat.
-Endothermic process: +q
-Temperature of surroundings Decreases energy is a reactant
products contain > energy than reactants Exothermic Reactions Endothermic Reactions energy is a product
products contain < energy than reactants E absorbed < E released - value E absorbed > E released + value VOCAB: System vs Surroundings HOMEWORK system/surroundings?
endothermic/exothermic? V: (SPOILER) Enthalpy (H) : the total amount of energy stored in a substance's particles;
also can be thought of as change in energy or
heat plus the work heat does in a system
often treated like heat V: heat capacity: heat needed to increase temp 1C:

what factors would influence the amount of heat needed? Calorie ~The unit of heat.
~The amount of heat needed to raise the temperature of one gram
of water one degree Celsius.
~A "Food Calorie" is 1000 calories, or a Kilocalorie Specific Heat (C) upper case! What's the Difference? Heat Capacity: heat per temperature change
Spec. Heat: heat per MASS and per temperature change Specific Heat Calculations Calculate the energy required to heat a beaker of water at 18 °C to boiling. The mass of the water is 70.0 g.
(C pure water = 4.184 J/g°C) - Specific Heat can be used to calculate heat changes in endo/exothermic processes Think Fast! What's the C of water?
(in cal/gºC) NOTE: q = m C T can always be rearranged to solve for other unknowns


This is the capital version of the Greek letter Delta (take a look at the Delta Airlines logo sometime)
Delta is used in science to indicate a change from one point to the next.

Therefore:
Delta T = the final temp - initial temp HOMEWORK #3 #4 —Robert Frost HOMEWORK Heat required to raise 250 g of Hg 52ºC?
C of Hg = 0.033 cal/gºC KEY Question q=mC(tf-ti) Heat(J) Mass(g) Heat
Capacity(J/g.K) Change in temp(K or C) Heat Equation Breakdown Write-in Poll http://www.polleverywhere.com/free_text_polls/B9eyb1gwEEs2E8F Write-in Poll http://www.polleverywhere.com/free_text_polls/B9eyb1gwEEs2E8F Write-in Poll http://www.polleverywhere.com/free_text_polls/B9eyb1gwEEs2E8F http://www.polleverywhere.com/multiple_choice_polls/LTE2Njc4OTUzMDM Multiple Choice what does the heat capacity of an object depend on? KEY Question What are some ways in which energy changes can occur? KEY Question what happens to the energy of the universe during a chemical or physical process? 1st Law of Thermodynamics:
energy cannot be created or destroyed, only transformed food energy is mainly derived from breaking C-H bonds Brett McMillan Notes on Notes Agenda Introduction Today, we will cover the first half of Chapter 17: Thermochemistry
discuss concepts
answer key questions
practice problems & review homework #1-4 Polling Who Wore It Better? A B C D 24 J 5740 J 24,016 J 5.74 kJ there are two kCal in the average raisin.
a joule is roughly equivalent to the energy needed to lift an apple off the ground... Write-in Poll http://www.polleverywhere.com/free_text_polls/B9eyb1gwEEs2E8F Write-in Poll http://www.polleverywhere.com/free_text_polls/B9eyb1gwEEs2E8F http://www.polleverywhere.com/multiple_choice_polls/LTE2Njc4OTUzMDM Multiple Choice kCal!!! calorimetry: the study of measuring the heat of chemical reactions calorimeter: device used to measure heat involved in a chemcial reaction when heat is transfered from one substance to another, the amount of heat LOST by the HOT object equals the amount of heat GAINED by the COLD object Therefore: q + q = 0 lost gained Heat Transfer RXN! RXN! Exothermic Reaction Endothermic Reaction RXN! Surroundings System calorimeter - Surroundings: gain heat
- System: loses heat - Surroundings: loses heat
- System: gains heat Different 'Flavors' of Enthalpy enthalpy is used in calculating energy changes during chemical reactions, phase changes, and combustion (which is a kind of chemical reaction). The energy absorbed or released as heat in a chemical or physical change is measured in a calorimeter. is commonly used to calculate the specific heat of a material Calorimetry Coffee cup calorimeter The amount of heat transferred as energy is usually measured in joules (J), the SI unit of heat as well as other forms of energy Calorimetry Heat of Reaction The quantity of energy released or absorbed as heat during a chemical reaction
Difference between the stored energy of the reactants and products Thermochemical Equations We show the heat of reaction using a thermochemical equation; a chemical equation that includes the quantity of energy released or absorbed as heat. Examples: Endothermic Exothermic Energy is released 2H + O 2H O + 483.6 kJ 2 (g) 2 (g) 2 (g) H = negative 2H + O 2H O H = -483.6 kJ/mol 2 (g) 2 (g) 2 (g) Energy is gained or absorbed 2H O + 483.6kJ 2H + O 2 (g) 2 (g) 2 (g) Enthalpy (H) Enthalpy is the heat content of a system at constant pressure
Enthalpy cannot be measured but change in enthalpy
( H) can.
Change in Enthalpy ( H) is the amount of energy absorbed or lost by a system as heat during a process at constant pressure.
H = H - H
Thermochemical equations are usually written by designating the value of H rather than writing the energy as a reactant or product. products reactants 2H O 2H + O H = 483.6kJ/mol H = positive 2 (g) 2 (g) 2 (g) What's Temperature then? (mnemonic: your 'ex' is someone you release or subtract from your life ) (mnemonic: you add energy 'endo' de process.) #1 #2 ~The ability of a substance to absorb heat. The amount of energy required to raise the temperature of one gram of a substance by one degree Celsius Formula: C or c = specific heat at given pressure
q = energy lost or gained
m = mass of sample
T = Difference between initial and final temperature p m x T C = q q = C x m x T The amount of heat required to raise the temperature of a unit _______ of a material by 1oC is called its specific heat capacity.
211374 A weight

211592 B volume

217788 C mass If the temperature of 80 g of copper [having a specific heat capacity of 0.4 J/(g oC)] is lowered by 10oC, then the heat lost by the copper is
211374 A 4.0 J

211592 B 320 J

217788 C 32 J

217792 D 800 J How does a calorie compare to a joule?
A. A calorie is smaller than a joule.
B A calorie is equal to a joule.
C. A calorie is larger than a joule.
D The relationship cannot be determined. When energy is changed from one form to another, ____.
211374 A: all of the energy can be accounted for

211592 B: a physical change occurs

217788 C: all of the energy is changed to a useful form

217792 D: some of the energy is lost entirely 211374 A

211592 B

217788 C

217792 D Energy Kinetic Potential "Virtually every chemical reaction is accompanied by a change in energy" Conservation of Energy Thermal The energy possessed by an object due to its motion. Energy stored within bonds of chemical compounds
Chemical energy is released in a chemical reaction. Stored Energy. In Chemistry, it is associated with the arrangement of particles Energy that comes from the moving or vibrating of molecules (heat) States that energy may neither be created nor destroyed The ability/capacity of a system to do work V for vocab. | Key Questions | homework | you will have access to this the average kinetic energy of the particles in a substance Short Answer:
pollev.com
274798 then answer Multiple Choice:
pollev.com/bamcmillan
ENERGY
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