Thermochemistry
description
Transcript of Thermochemistry
![Page 1: Thermochemistry](https://reader036.fdocuments.in/reader036/viewer/2022062521/56816688550346895dda3d15/html5/thumbnails/1.jpg)
Thermochemistry
• the study of the transfer of energy between reacting chemicals and their surroundings
![Page 2: Thermochemistry](https://reader036.fdocuments.in/reader036/viewer/2022062521/56816688550346895dda3d15/html5/thumbnails/2.jpg)
Energy
• the ability to do work OR the capacity to produce change
• measured in J or kJ• Has many forms but the 2 main forms are
potential energy and kinetic energy
![Page 3: Thermochemistry](https://reader036.fdocuments.in/reader036/viewer/2022062521/56816688550346895dda3d15/html5/thumbnails/3.jpg)
Potential Energy-the energy possessed by a body because of its position (stored
energy)
![Page 4: Thermochemistry](https://reader036.fdocuments.in/reader036/viewer/2022062521/56816688550346895dda3d15/html5/thumbnails/4.jpg)
Kinetic Energy-the energy of motion
-the greater the motion the greater the KE
![Page 5: Thermochemistry](https://reader036.fdocuments.in/reader036/viewer/2022062521/56816688550346895dda3d15/html5/thumbnails/5.jpg)
Potential energy can be converted to kinetic energy and vice versa
![Page 6: Thermochemistry](https://reader036.fdocuments.in/reader036/viewer/2022062521/56816688550346895dda3d15/html5/thumbnails/6.jpg)
PEKE
![Page 7: Thermochemistry](https://reader036.fdocuments.in/reader036/viewer/2022062521/56816688550346895dda3d15/html5/thumbnails/7.jpg)
PEKE
![Page 8: Thermochemistry](https://reader036.fdocuments.in/reader036/viewer/2022062521/56816688550346895dda3d15/html5/thumbnails/8.jpg)
First Law of Thermodynamics (aka Law of Conservation of Energy)
Energy can neither be created nor destroyed but may be converted from one form to another
![Page 9: Thermochemistry](https://reader036.fdocuments.in/reader036/viewer/2022062521/56816688550346895dda3d15/html5/thumbnails/9.jpg)
In theory, all forms of energy can be converted from one form to another
![Page 10: Thermochemistry](https://reader036.fdocuments.in/reader036/viewer/2022062521/56816688550346895dda3d15/html5/thumbnails/10.jpg)
Chemical Energy
• Is a form of potential energy because it is based on the position of atoms in a substance
• Different types of atoms and different arrangement of atoms results in the storage of different amounts of chemical energy
• During a chemical reaction, chemical energy may be 1) stored 2) released as heat 3) converted to another form of energy
![Page 11: Thermochemistry](https://reader036.fdocuments.in/reader036/viewer/2022062521/56816688550346895dda3d15/html5/thumbnails/11.jpg)
Thermal Energy
• Is a form of kinetic energy • Is the energy associated with the random
motion of atoms and molecules• Can be calculated from temperature
measurements BUT does not equal temperature
![Page 12: Thermochemistry](https://reader036.fdocuments.in/reader036/viewer/2022062521/56816688550346895dda3d15/html5/thumbnails/12.jpg)
Thermal energy increases with temperature
![Page 13: Thermochemistry](https://reader036.fdocuments.in/reader036/viewer/2022062521/56816688550346895dda3d15/html5/thumbnails/13.jpg)
Heat (q)
• Is the transfer of thermal energy from one object to another due to temperature differences i.e. from a hot object to a cold object
• An object possesses thermal energy but it does not possess heat
• When referring to heat, i.e. the transfer of thermal energy, the terms “heat absorbed” and “heat released” are used
![Page 14: Thermochemistry](https://reader036.fdocuments.in/reader036/viewer/2022062521/56816688550346895dda3d15/html5/thumbnails/14.jpg)
Temperature
• Is proportional to the average kinetic energy of the particles of a substance i.e. the faster the particles move, the higher the temperature of the substance
• In chemistry, temperature is measured in Celsius or Kelvin
![Page 15: Thermochemistry](https://reader036.fdocuments.in/reader036/viewer/2022062521/56816688550346895dda3d15/html5/thumbnails/15.jpg)
Converting from Celsius to Kelvin oC +273= K
![Page 16: Thermochemistry](https://reader036.fdocuments.in/reader036/viewer/2022062521/56816688550346895dda3d15/html5/thumbnails/16.jpg)
Thermal properties of substances-describe the ability of a substance to absorb heat without changing
chemically
Specific heat capacity (c)• is the amount of heat energy required to raise
the temperature of 1 gram of a substance by 1oC
• Units: J/goC• Unique for each substance• cwater = 4.18 J/goC cAl = 0.900 J/goC
![Page 17: Thermochemistry](https://reader036.fdocuments.in/reader036/viewer/2022062521/56816688550346895dda3d15/html5/thumbnails/17.jpg)
Thermal properties cont’d
Heat capacity (C)• The amount of heat energy required to raise the
temperature of a given quantity of a substance by 1 oC
C = mc Q? What is the heat capacity of 15 g of water?Q? How much heat is required to raise the temperature of 3.0 g of water by 10oC?Q? How much heat is required to raise 3.0 g of aluminum by 10oC?
![Page 18: Thermochemistry](https://reader036.fdocuments.in/reader036/viewer/2022062521/56816688550346895dda3d15/html5/thumbnails/18.jpg)
q=mcΔT
On a mountaineering expedition, a climber heats water from 0oC to 50oC. Calculate the mass of water that could be warmed by the addition of 8.00 kJ of heat.
![Page 19: Thermochemistry](https://reader036.fdocuments.in/reader036/viewer/2022062521/56816688550346895dda3d15/html5/thumbnails/19.jpg)
Some more terminology:
System: the components of a chemical reaction i.e. the reactants
Na + H2O Surroundings: everything outside of the system i.e. the beaker the sodium and water are sitting in, the air
![Page 20: Thermochemistry](https://reader036.fdocuments.in/reader036/viewer/2022062521/56816688550346895dda3d15/html5/thumbnails/20.jpg)
More terminology cont’d
Exothermic Reactions: chemical reactions that produce heat; that is, heat is released from the system to the surroundings OR energy flows out of the systemEndothermic Reactions: chemical reactions that absorb heat; that is, the surroundings supply heat to the system OR energy flows into the system
![Page 21: Thermochemistry](https://reader036.fdocuments.in/reader036/viewer/2022062521/56816688550346895dda3d15/html5/thumbnails/21.jpg)
Enthalpy of a Reaction
• The energy absorbed from or released to the surroundings when reactants change to products
• Written as: ΔH (delta H)• Read as enthalpy of a reaction OR enthalpy
change OR heat of a reaction• Units: J or kJ• Can be determined by measuring the changes in
energy of the surroundings
![Page 22: Thermochemistry](https://reader036.fdocuments.in/reader036/viewer/2022062521/56816688550346895dda3d15/html5/thumbnails/22.jpg)
Calorimetry
• The experimental process of measuring the amount of heat absorbed or heat released in a chemical reaction
• Makes use of a calorimeter – a device such as a styrofoam cup that contains water- and a thermometer, to catch the heat being released from a reaction or to supply heat to the reaction
![Page 23: Thermochemistry](https://reader036.fdocuments.in/reader036/viewer/2022062521/56816688550346895dda3d15/html5/thumbnails/23.jpg)
Simple Styrofoam Calorimeter
![Page 24: Thermochemistry](https://reader036.fdocuments.in/reader036/viewer/2022062521/56816688550346895dda3d15/html5/thumbnails/24.jpg)
Pop Can Calorimeter
![Page 25: Thermochemistry](https://reader036.fdocuments.in/reader036/viewer/2022062521/56816688550346895dda3d15/html5/thumbnails/25.jpg)
Bomb Calorimeter