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Thermochemistry. Energy Changes. Energy. The ability to do work Types of energy chemical, mechanical, light, heat, electrical, sound. Law of Conservation of Energy. Energy cannot be created or destroyed It only changes from one form to another.
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Energy • The ability to do work • Types of energy • chemical, mechanical, light, heat, electrical, sound
Law of Conservation of Energy • Energy cannot be created or destroyed • It only changes from one form to another
Almost all chemical reactions have a change in energy • Energy can be added (endothermic) • Energy can be given off (exothermic) • Thermochemistry studies those changes and their effects
A chemical reaction that releases energy is exothermic, and the energy of the products is less than the energy of the reactants.
In an endothermicreaction, the products have a larger energy than the reactants, and the reaction absorbs energy.
Remember • Temperature is the average kinetic energy of a substance • Measured in Kelvins (K) • Heat is the energy transferred during a reaction • Measured in Joules (J) • Always moves from high temperature to low temperature
Heat and Temperature • The energy absorbed or released as heat is measured in a calorimeter. • Known quantities of reactants are sealed in a reaction chamber that is immersed in a known quantity of water. • Energy given off by the reaction is absorbed by the water, and the temperature change of the water is measured. • From the temperature change of the water, it is possible to calculate the energy as heat given off by the reaction.
Specific Heat • The amount of energy transferred depends on • the kind of material involved • on its mass. • The specific heat of a substance is the amount of energy required to raise the temperature of one gram by 1°C or 1 K. • Materials with a high specific heat absorb more energy before their temperature changes
Specific Heat Problems • energy gained or lost with a change of temperature can be calculated using the following equation.
A 4.0 g sample of glass was heated from 274 K to 314 K, a temperature increase of 40. K, and was found to have absorbed 32 J of energy as heat. • 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?
If 220.0g of steam at 350.0 °C absorbs 550.0 kJ of heat energy, what will be its increase in temperature? What is it’s final temperature?
When 80.0 grams of a certain metal at 90.0 °C was mixed with 100.0 grams of water at 30.0 °C, the final equilibrium temperature of the mixture was 36.0 °C. What is the specific heat (J/g °C) of the metal?