Thermochemistry is the study of energy changes that occur during chemical reactions and phase changes (changes of state)
The Nature of Energy Energy-are we running out?! Energy is the ability to do work or produce heat Energy-are we running out?! Click on the link to watch the video
flows due to temperature differences Energy flows from high to low until… System E E E E E System E E E E E the system reaches dynamic equilibrium Energy is transferred from one system to the other, this is heat. flows due to temperature differences (always hot to cold)
Law of Conservation of Energy (aka 1st Law of Thermodynamics) Energy cannot be created nor destroyed; only converted into different types.
Kinetic vs. Potential Energy Two main types of energy – kinetic and potential Kinetic – energy of motion Potential – energy due to position or energy stored in chemical bonds
Kinetic vs. Potential Energy
Kinetic Energy Thermal energy : comes from heat Electric: caused by moving electric charges Sound: energy produced by the periodic movement of matter
Potential Energy Chemical: energy stored in a substance because of its composition Example: gasoline has lots of C-H bonds to break Nuclear: nuclear fission or fusion produce energy Gravitational-positional energy in a gravitational field (not the same as gravity)
Temperature vs. Heat Temperature: a measure of the motion in a sample a measurement of heat. Heat : total energy of molecular motion, dependent upon amount, size, and type of particles. Heat is energy.
Symbol and Units for heat For heat we will be using little “q” Heat is energy Heat = q Units for heat (q) are: calories: little calories for science (cal) Calories: Nutritional Calories (C) Joules: SI unit of heat(J)
Definition of scientific calorie calorie - the amount of heat required to raise the temperature of one gram of pure water by one degree Celsius.
Converting Energy Units Calorie/calorie/kilocalorie calorie/Joule 1 C = 1000 cal = 1 kcal 1 cal = 4.184 J You may write these conversions on your formula sheets
The molecules of the thermometer in hot water should be randomly arranged, slightly further apart, moving faster. The molecules of the thermometer in cold water should be randomly arranged, closer together, moving slower. The molecules of the thermometer in hot water should be randomly arranged, slightly further apart, moving faster. The molecules of the thermometer in cold water should be randomly arranged, closer together, moving slower.
Example 1 A cereal has 155 nutritional Calories per serving. How many calories, kilocalories and Joules is this?
Example 2 A person on a diet consumed 1350 Calories in one day. How many calories, kilocalories and Joules is this?