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Transcript of Thermochemistry. Thermodynamics Study of energy transformations Thermochemistry is a branch of...
![Page 1: Thermochemistry. Thermodynamics Study of energy transformations Thermochemistry is a branch of thermodynamics which describes energy relationships in.](https://reader036.fdocuments.us/reader036/viewer/2022081507/5a4d1b417f8b9ab0599a1146/html5/thumbnails/1.jpg)
Thermochemistry
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Thermodynamics
Study of energy transformations Thermochemistry is a branch of
thermodynamics which describes energy relationships in chemical reactions
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Energy
Capacity to do work or to transfer heat Mechanical work (w) is the product of force (F)
operating on an object and the distance (d) through which it moves
W = F x d Energy is required to do work
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Heat (Q)
Heat is the energy transferred from one object to another due to a difference in temperature
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Forms of Energy
Kinetic Energy – energy of motion- magnitude depends on the mass of the object and its velocity- EK = ½ m v2
- both mass and speed determine how work it can do
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Potential Energy – stored energy Other forms of energy are simply types of
kinetic or potential on an atomic or molecular level
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Energy Units
Joule (J) 1J = 1 kg m2/ s2
A calorie (cal) is the amount of energy required to raise the temp of 1 g of water 1 ºC
1 cal = 4.184 J
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Example
A 145 g baseball is thrown with a speed of 25 m/s. Calculate the kinetic energy in Joules.
What is the kinetic energy in calories?
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Systems
Portion we single out for study Surroundings is everything else outside the
system When studying energy changes in a chemical
reaction, the reactants and products are the system and everything else is the surroundings
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Law of Conservation of Energy
Energy can be converted from one form to another but cannot be created or destroyed
Also called “First Law of Thermodynamics”
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Internal Energy
Total energy of a system – sum of kinetic and potential energies
Cannot determine exact internal energy Can only determine a change in internal
energy ΔE = Efinal – Einitial
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If ΔE is positive there is a gain in internal energy in the system
If ΔE is negative the system lost energy to its surroundings
Higher energy systems tend to lose energy and are therefore less stable
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Heat and Work
Any system can exchange energy with surroundings in two ways – as heat or work
Internal energy increases as heat is added to or work is done on a system
ΔE = Q + wQ is positive if heat is added to systemw is positive if work is done on the system
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Heat Changes
Exothermic Reactions – when heat is given off by the reaction (-Q)
Endothermic Reactions – when heat is used by the reaction (+Q)
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Example
As a combustion reaction occurs the system loses 550 J of heat to its surroundings and it does 240 J of work in moving a piston. What is the change in its internal energy?
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State Function
These are systems for whom the value of ΔE does not depend on the previous history of the sample, only on the present condition
Energy is a state function Work and heat are not state functions
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