Chapter 16 Reaction Energy Thermochemistry I can define temperature and state the units in which it...
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Transcript of Chapter 16 Reaction Energy Thermochemistry I can define temperature and state the units in which it...
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Chapter 16 Reaction Energy Thermochemistry
I can define temperature and state the units in which it is measured I can define heat and state its units.I can perform specific-heat calculations.
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What is thermochemistry?
…. the study of the transfer of energy as heat that accompany chemical reactions and physical changes.
www.scilinks.orgTopic: Heat/TemperatureCode: HC60726
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Temperature and Heat
Temperature is a measure of the average kinetic energy of the particles in a sample of matter.
Temperature is measured with a thermometer.
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Celsius Freezing\melting 0⁰C Boiling 100⁰C
⁰C = K - 273
Kelvin Freezing\melting 273K Boiling 373K
K = 273 + ⁰C
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Fahrenheit vs. Celsius
Celsius vs. Kelvin
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The amount of energy transferred as heat is usually measured in joules, J.
A joule is the SI unit of heat as well as all other forms of energy.
J = N x m = kg x m2
s2
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Calorimeter – Devise used to measure the energy absorbed or released as heat in a chemical or physical change.
Simple Coffee Cup Calorimeter
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Heat – The energy transferred between samples of matter because of a difference in their temperatures.
Energy transfersfrom warmer objects to coolerobjects.
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SPECIFIC HEAT… the amount of energy required to raise the temperature of one gram of a substance by one Celsius degree 1⁰C) or one Kelvin (1K).
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So… if you have a high specific heat value, what does that mean by definition?
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http://www.chem1.com/acad/webtext/chembond/cb01.html#SEC1http://www.chem1.com/acad/webtext/chembond/cb01.html#SEC1
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cp = q
m x T
cp = specific heat at constant pressure
q = heat energy lost or gained
m = mass of the sample
T = difference between the initial and final temperatures
q = cp x m x T
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Sample problem A, page 533
A 4.0 g sample of glass was heated from 274 K to 314 K, a temperature increase of 40.0 K , and was found to have absorbed 32 J of energy as heat energy. a.What is the specific heat of this type of glass?b.How much energy will the same glass sample gain when it is heated from 314 K to 344 K?
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Practice, page 5341.Determine the specific heat of a material if a 35 g sample absorbed 96 J as it was heated from 293 K to 313 K.
2.If 980 J of energy are added to 6.2 g of a substance at 291 K. The final temperature is 311K. What is the specific heat of this substance.
Additional practicego.hrw.com keyword HC6NRGX
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Enthalpy of Reaction
Enthalpy change is the amount of energy absorbed by a system as heat during a process at constant pressure. H, change in enthalpy.
Enthalpy for a reactionH = H products – H reactants
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Enthalpy of reaction…. is the quantity of energy transferred as heat during a chemical reaction.
Exothermic - energy is released (given off) feels warm
Endothermic – energy is absorbed (taken in) feels cool
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Thermochemical Equation … an equation that includes the quantity of energy released or absorbed as heat during the reaction as written.2H2 (g) + O2 (g) 2H2O(g) + 483.6 kJ
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In an exothermic chemical reaction the enthalpy change is negative meaning energy is released from the system as heat
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In an endothermic chemical reaction the enthalpy change is positive meaning energy is absorbed into the system as heat
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Driving Force of Reactions
Learning Target: I can explain the relationship between enthalpy change and the tendency of a reaction to occur.
I can explain the relationship between entropy change and the tendency of a reaction to occur.
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Driving Force of Reactions
The change in energy of a reaction system is one of two factors that allow chemists to predict whether a reaction will occur spontaneously and to explain how it occurs.The randomness of the particles in a system is the second factor affecting whether a reaction will occur spontaneously.
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Entropy
Entropy, S, is the tendency toward randomness.
It is defined as a measure of the degree of randomness of the particles such as molecules, in a system
www.scilinks.orgTopic: Entropy Code: HC60523
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Solid – particles are fixed in position – degree of randomness is low – low entropy
Liquid – particles can move – system more random – higher entropy
Gas – particles moving rapidly – most random – highest entropy