Chemistry Module 6

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Module Six: Thermochemistry and rate
Study sheet for the test

G.01: Thermo-chemistry
I. Temperature and Thermal Energy
Temperature is a measure of the average kinetic energy of the particles in a sample of matter. The greater the avg. kinetic energy of the particles in a sample of matter, the higher the temperature of that matter. Some temperature scales are Fahrenheit, Celsius and Kelvin. Thermal energy is the measure of the total kinetic energy in a sample. And Temperature is a measure of the average kinetic energy.

Ex: Which container (the bath tub or the coffee cup) have a temperature that is higher than the other? The temperature of the coffee cup is higher!
Which sample of water has a greater amount of thermal energy? The bathtub. Even though the avg. kinetic energy of the particles in the coffee cup is higher than the avg.KE of the particles in the bathtub, the thermal energy in the warm bath tub is higher because there are more particles in the tub than the cup.

II. Heat
Heat is the movement, or flow, of thermal energy.
Heat always flows spontaneously from matter at a higher temperature to matter at a lower temperature. Heat and thermal energy are both measure in units of energy, the SI unit for energy is Joule(J). Another unit of energy that is commonly used is the Calorie. The food calorie means that for every one food calorie that is eaten has enough thermal energy to increase the temperature of 1000 grams of water by 1 degree Celsius.

III. Closed, open and isolated systems
In science, it is important to identify the system being observed or investigated. Some examples of systems are: atom, reaction, cell, ecosystem, universe etc. In chemistry, the system is only defined as the chemical reaction or physical change being examined. a. Isolated systems

The total amount of energy and matter contained in an isolated system will remain constant because energy and matter cannot leave or enter. Ex: Universe, space
b. Closed systems
Energy can leave or enter the system but matter cannot.
Ex: earth, beakers
c. Open system
Both energy and matter are exchanged freely.
Ex: our body.

IV. Energy in Chemistry
The role of energy in chemical and physical change: virtually every process involves absorption or release of energy. The law of conservation says that energy remains constant during a reaction Thermochemistry is the study of the changes in energy that accompany chemical reactions and physical changes.

6.02: Endothermic and Exothermic
I. Intro
Endothermic: A chemical or physical change that absorbs energy from the surroundings. Exothermic: a chemical or physical change that releases energy to the surroundings.

II. Endothermic reactions
The temperature of an object can be used to determine whether heat has moved into or out of an object. * D and boiling are both endothermic processes because both require energy to be absorbed from the surroundings for the process to occur. Ex: when sweat evaporates from your skin, your skin feels cooler. This is because the TE from your skin flows into the liquid (sweat), raising the temperature until it evaporates. The TE↓and the skin is cooler. * Photosynthesis involves endothermic reactions that require energy from the sun.

III. Exothermic Reactions
The amount of energy released by an exothermic reaction depends on the amount of reactants as well as the dif. In P.E of the reactants and products The products have a ↓P.E than the reactants.
Ex: hot packs, ice cubes

IV. Potential energy diagrams
This diagram is used to represent the general change in energy over the course of a reaction. a. Exothermic
In an exothermic reaction, the products have less potential energy than the reactants had at the beginning of the reaction. This is why the potential energy diagram for an exothermic reaction starts at a higher energy value and ends at a lower energy value. The law of conservation of...
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