Work on exam study guide. Closed toe shoes Tues. 5/11/15 Do Now Copy and answer the questions 1) Explain how particles transfer kinetic energy from one particle to another. Energy is transferred during collisions. 2) Using what you know about thermal energy, explain how a thermos keeps hot coffee hot. The vacuum prevents particles in the hot coffee from colliding with particles in the surroundings. This keeps the energy within the container. 1) Energy Ch. 15.1 p. 516-8 a) Energy can be modeled as a substancelike quantity that can be measured and stored in a physical system. b) Energy can “flow” or “transfer” from one system to another and cause physical or chemical changes. c) Energy maintains its identity after transfer. 2) Kinetic Molecular Theory (KMT) Ch. 12.1 p. 402-3 a)Matter is made of tiny particles that are in constant random motion. https://www.youtube.com/watch?v=hy-clLi8gHg b) These particles exert long-range attractions and short-range repulsions on one another. Attractions reduce the energy in the system; repulsions increase the amount of energy. c) A hotter sample is one whose molecules are moving (on average) faster than the molecules in a colder sample. 3) Storing Energy a) Thermal energy, Eth – energy of motion. Eth depends on the mass of the object and velocity of the particles in the object b) Phase energy, Eph – energy due to attractions between molecules. Attractions decrease the energy of a system. Gases – weak attractions, high Eph Solids – strong attractions, low Eph c) Chemical potential energy, Ech- energy due to attractions of atoms within molecules. These attractions are described as chemical bonds because they are directed between specific atoms in the molecule. Exam Study Guide is available on Web Assign. 5/12/15 Do Now Copy and answer the questions Using what you know about thermal and phase energy, explain why sweating makes you feel cooler. When you sweat, water evaporates and changes from liquid to gas phase. The water vapor has higher Eph than liquid water. Energy is transferred from Eth to Eph and your body temperature decreases. Icy Hot : Energy and Phase Changes 1) The purpose is to measure the temperature of water as it warms and changes phase from solid to liquid to gas. 2) Hypothesis - What will the graph of temperature vs time look like? Draw a sketch of the curve. Label axes and include a title. Energy and phase change Temp(ºC) 100 0 Time Icy Hot : Energy and Phase Changes Icy Hot: 3) Procedures • Begin taking temperature readings when you turn on your hotplate. • Measure temperature every 30 s. • Before taking each reading, use a stirring rod to stir for 5 s. • Heat the water slowly (~350°C/4) until all the ice has melted. Then, increase the heating by turning up your hot-plate. • Stop taking temperature readings after your water has been at a rolling boil for 3 minutes. Exam Study guide due day of exam. 5/13/15 Do Now Copy and answer the questions 1) How are the structures of solid, liquid, and gaseous water similar? Different? 2) How does the arrangement of the particles explain the properties of the phase? Why is a particular phase rigid or fluid? 3) What forces attract particles to each other? What forces cause repulsions? 4) Processes that Transfer Energy a) heating (Q) - transfers energy between particles through collisions System what is being studied b) working (W) - transfers energy between big objects through forces c) radiating (R) - transfers energy by emitting or absorbing photons (light) surroundings d) Energy transfers affect both the system and the surroundings. e) Energy doesn’t mysteriously appear or get lost. Icy Hot Lab – Clean-up and Analysis Clean-up • Unplug your hotplate. Use tongs to empty beaker and place on the table. Make sure the cord is off the floor and away from the sink. • Allow beaker to cool. Return materials to your basket. 4) Analysis - Construct a graph of temperature vs. time of your data. Connect the dots with a smooth curve. Icy Hot Lab – Clean-up and Analysis 4) Analysis - Construct a graph of temperature vs. time of your data. Connect the dots with a smooth curve. From Ice to Steam B A C Icy Hot: Analysis and Conclusion Divide your heating curve into three regions; label (A) a low temperature plateau (B) a region of temperature change (C) a high temperature plateau C B A Answer the following questions on the same paper as your pre-lab. 1. i. Did a chemical change occur during heating and phase change? Explain. ii. Did the system absorb or release energy? Explain. 2. For each region (A, B, and C) on your graph, i. describe how the energy supplied by the hotplate was stored by the system (Eth or Eph) ii. state which phases were present iii. draw a model at the molecular level that shows how the water molecules were behaving. 3. How would increasing the rate of heating by turning up the hotplate affect the shape of the temp. vs. time curve?