Unit 4 Thermodynamics- Lecture 2: PS 1-4: Develop a model to illustrate that the release or absorption of energy from a chemical reaction system depends upon the changes in total bond energy. a. Students know how to describe temperature and heat flow in terms of the motion of molecules (or atoms). b. Students know chemical processes can either release (exothermic) or absorb (endothermic) thermal energy.

Unit 4 Lecture 2: Temperature and Heat

Unit 4 Lecture 2: d. They are all sitting at the same ambient temperature so they will have the same average kinetic energy.

Unit 4 Lecture 2: Energy Initial model Come up with a model to show what would happen if you take two equal amounts of water, one at 00C and one at 1000C and mix together. Remember models both show what happens and explain WHY! Show what happens at the macroscopic (visual) and particle levels

Heat: A form of energy that flows from a warmer object to a cooler object. The warmer object loses heat and becomes colder (temperature lowers) The colder object absorbs heat and become warmer (temperature rises)

Measuring Heat energy: Three major energy units: Joule (J), calorie (cal), Food Calorie (Cal) 1 calorie = 4.184 joules Food Calories are equivalent to kilocalories (Kcal) 1 Calorie = 1 Kcal= 1000 calories

Example #1 Convert 60.1 cal to joules 19

Example #1 Convert 60.1 cal to joules 1 cal = 4.184 joules 60.1 cal x 4.184 J = 1 cal = 251 J 19

Example #2 A reaction released 8650 joules, how many Food Calories of energy are released? 19

Example #2 A reaction released 8650 joules, how many Food Calories of energy are released? 1 cal = 4.184 joules, 1000 cal = 1 Cal 8650 J x _1 cal x 1 Cal = 4.184 J 1000 cal = 2.07 Calories 19

Temperature: A measure of the average kinetic energy of the particles in a sample of matter. - We measure in K or 0C

An example of Heat transfer between two boxes. Watch the heat flow PowerPoint and come up with a model of what happened to the boxes when they came in contact. Remember a model shows what happens and why. This should include information at the macroscopic and particle levels. Heat Flow PowerPoint

PhET Energy Forms and Changes Do the PhET activity.

Virtually every reaction either releases or absorbs heat. Thermochemistry: Study of heat changes in reactions Law of conservation of energy: Energy is neither created nor destroyed within the universe The universe consists of the system and the surroundings. System: the reacting particles Surroundings: everything else including all non-reacting particles.

Chemical Energy: Is the energy within bonds in chemical compounds (form of potential energy) When bonds break they absorb energy (endothermic) When bonds form they release energy (exothermic)

Exothermic and Endothermic Reactions: All Chemical reactions require breaking bonds which absorbs energy and making bonds which releases energy. The overall change in energy results in a reaction that is either Exothermic or Endothermic. - always from the view of the system

Potential Energy of Reactants vs. Products

Products have less potential energy so Exothermic

Examples…. *It feels HOT because surroundings heat up Exothermic:A process that has an overall release of energy *It feels HOT because surroundings heat up Reactants  Products + ENERGY Examples…. O2 + H2  H2O + energy SnCl2(s) + Cl2 (g)  SnCl4 (s) + 186KJ Burning sugar Rusting iron Mixing acid and water Water condensing

Examples…. *It feels COLD because surroundings cool down Endothermic: A process that has an overall absorption of energy *It feels COLD because surroundings cool down Reactants + ENERGY  Products Examples…. Sunlight + CO2 + H2O  C6H12O6 + O2 N2(g) + O2 (g) + 180KJ  2NO (g) Producing sugar by photosynthesis Forming a cation from a gaseous atom Baking bread evaporation