Major Concepts• Types of Energy
• Work Formula • Temperature • Heat • Exothermic vs Endothermic • Law of Conservation of Energy • 1st and 2nd Law of Thermodynamics • Calculating Specific Heat • Hess's Law FORMULASWork Formula: Work = Force x Distance
**If you push against a table and it doesn't move, you are not doing work. Why? Work = Force x Distance. You didn't make the table go any distance. Specific Heat Formula: Q = mc∆t What do all those variable stand for? Q stands for heat, or energy. It is measured in Joules. m stands for mass. It is measured in grams ∆t stands for "change in temperature" **Use this formula in specific heat problems! |
Example Problems1. Calculate the heat capacity of a piece of wood if 1500.0g of wood absorbs 6.75x10^4J of heat, and its temperature changes from 32ºc to 57ºc.
Answer: 1.8 J/gºc 2. How much heat in kilojoules has to be removed from 225g of water to lower its temperature from 25.0ºc to 10.0ºc? Answer: -14.1 kJ 3. Use Hess's law to determine the ∆H for the overall equation: overall: 2NOCl ---> 2NO + Cl2 ∆H= ??? 1) 2NO --> N2 +O2 ∆H= -180.5 kJ 2) N2 + O2 ----> 2NOCl ∆H= 103.4 Answer: ∆H= 77.1 kJ 4. According to your answer for #3, was the reaction endothermic or exothermic? Answer: endothermic, because the ∆H was positive. 5. What three things are needed for spontaneous reactions to occur? Answer: Entropy, Enthalpy, and Kinetic Energy |
EXOTHERMIC VS. ENDOTHERMIC
Exothermic= Heat Leaving
Endothermic= Heat required/entering
TYPES OF ENERGY
-Potential: chemical, elastic, and gravitational
-Kinetic
Potential energy is simply "stored" energy.
Kinetic energy is the energy of motion.
Note: All compounds will have Potential energy because of bonds
Online Resources
Laws of Thermodynamics AND Potential vs. Kinetic Energy: http://www.emc.maricopa.edu/faculty/farabee/biobk/biobookener1.html
Explanation of Hess's Law: http://www.science.uwaterloo.ca/~cchieh/cact/c120/hess.html
Explanation of Hess's Law: http://www.science.uwaterloo.ca/~cchieh/cact/c120/hess.html
Video Resources
Specific Heat Capacity Tutorial/Explanation: http://www.youtube.com/watch?v=eIBVimdYnDI
Hess's Law Video(By Me!): https://vimeo.com/60607918
Hess's Law Video(By Me!): https://vimeo.com/60607918
Activity Resources
Specific Heat Activity: http://www.algebralab.org/practice/practice.aspx?file=Algebra_SpecificHeatCapacity.xml
Hess's Law Activity: http://chemistry2.csudh.edu/lecture_help/Hesslaw.html
Hess's Law Activity: http://chemistry2.csudh.edu/lecture_help/Hesslaw.html