Energy and Chemical Changesection 1  Energy

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Name:……………………………………………
Grade: ………………………………..
Subject: Chemistry
Date: …………………………………………
Chapter 15 : Energy and Chemical Change
Section 1: Energy
The Nature of Energy
 Energy : is the ability to do work or produce heat.
 It exists in two basic forms: potential energyand kinetic energy.
 Potential energy is energydue to the compositionor position of an object.
 Kineticenergy is energy of motion.
 Chemicalsystems contain both Kinetic energyand potential energy.
 Kinetic energy of a substance is directly related to its motion, which is directly
proportional to temperature..
 The potential energy of a substance depends on its composition. ( the type of atoms
and type of chemical bonds)and the arrangement of the atoms.
 Law of conservation of energy :
States that in any chemicalreactionor physical process , energycan be
convertedfrom one form to another, but it is neither createdor destroyed .
 This is also known as the first law of thermo dynamic

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 Chemical potentialenergy:
 The energythat is stored in a substance because ofits composition.
 It has an important role in chemicalreactions.
 Example:
The potential energy of propane C3H8 results from the arrangement of the
carbon and hydrogen atoms and the strength of the bonds that join them.
 Heat,
 When gasoline burns in an automobile’s engine, some of octane’s chemical
potential energy is converted to the work of moving the automobile,
 However, much of the chemical potential energy of octane is released as heat.
 Heat :
The energytransferred betweenobjects at different temperature.
 q is used to symbolize heat.
 Measuring Heat:
 A calorie (cal).
The amount of energy required to raise the temperature of one gram of pure
waterby one degree Celsius (1°C)
 The energy content of food is measured in Calories , or 1000 calories (kilocalorie).
 A joule (J) ;
Is the SI unit of heat and energy, equivalent to 0.2390 calories.
 One calorie equals 4.184 joules.
 Table 1 summarizes the relationships between calories, nutritional Calories, joules,
and kilojoules (kJ) and the conversion factors you can use to convert from one unit
to another.

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 SpecificHeat
 The specific heatof any substance is ;
The amount of heat required to raise the temperature of one gram of that
substance by one degree Celsius.
 Because different substances have different compositions , each substance has
its own specific heat.
 Some objects require more heat than others to raise their temperatures.
 Example:
 The specific heat (c) of water is 4.184 J/(g·°C),
 The specific heat of concrete is 0.84 J/(g·°C),
 Which means that the temperature of concrete increases roughly five times
more than water’s temperature when equal masses of concrete and water absorb the
same amount of energy.
Calculatingheat absorbed
Table 2 shows the specific heats for some common substances.

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 Calculatingheat released
 Substances can both absorb and release heat.
 The same equation for q, the quantity of heat, can be used to calculate the energy
released by substances when they cooloff.

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 EXAMPLEProblem 2
 The temperature of a sample of iron with a mass of 10.0 g changedfrom 50.4°C
to 25.0°C withthe release of114 J. What is the specific heat of iron?

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Using the Sun’senergy: Read textbook page 522.

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SECTION 1 REVIEW:
7. Explain how energy changes from one form to another in an exothermic reaction. In an
endothermic reaction.
8. Distinguish between kinetic and potential energy in the following examples:
two separated magnets; an avalanche of snow; books on library shelves; a
mountain stream; a stock-carrace; separation of charge in a battery.
9. Explain how the light and heat of a burning candle are related to chemical
potential energy.
10. Calculate the amount of heat absorbed when 5.50 g of aluminum is heated
from 25.0ºC to 95.0ºC. The specific heat of aluminum is 0.897 J/(g∙ºC).
11. Interpret Data Equal masses of aluminum, gold, iron, and silver were left to
sit in the Sun at the same time and for the same length of time. Use Table 2
to arrange the four metals according to the increase in their temperatures from
largest increase to smallest.

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