1 / 13

Chemistry – Oct 22 , 2018

Chemistry – Oct 22 , 2018. P3 Challenge – Distinguish between a triple point and a critical point. Turn in States Phet Activity if not yet Turn in PT Units HMK if not yet. Chemistry – Oct 22 , 2018. Objective – Energy and Heat Capacity Solutions and Solubility Assignments

lane-donaldson
Download Presentation

Chemistry – Oct 22 , 2018

An Image/Link below is provided (as is) to download presentation Download Policy: Content on the Website is provided to you AS IS for your information and personal use and may not be sold / licensed / shared on other websites without getting consent from its author. Content is provided to you AS IS for your information and personal use only. Download presentation by click this link. While downloading, if for some reason you are not able to download a presentation, the publisher may have deleted the file from their server. During download, if you can't get a presentation, the file might be deleted by the publisher.

E N D

Presentation Transcript

  1. Chemistry – Oct 22, 2018 • P3 Challenge – Distinguish between a triple point and a critical point. Turn in States Phet Activity if not yet Turn in PT Units HMK if not yet

  2. Chemistry – Oct 22, 2018 • Objective – • Energy and Heat Capacity • Solutions and Solubility • Assignments • Heat Worksheet • Agenda – • Energy • Heat • Heat Capacity • Heating Curve of Water (time permitting)

  3. What is Energy? • Energy = Ability to do work • Law of Conservation of Energy: Energy is neither created nor destroyed. • It can only be transformed from one form to another or transferred from one system to another. • Total energy of a system = Kinetic Energy + Potential Energy • Kinetic energy – Energy of motion • Potential energy – Stored energy

  4. Kinetic Energy Types • Thermal energy – Energy of random motion of atoms • Electromagnetic energy – Energy of light • Sound energy – Energy of motion of atoms due to pressure differences • Electrical energy – Energy of the flow of electrons

  5. Potential Energy Types • Gravitational potential energy – Energy of position within Earth’s gravity • Electrical potential energy – Energy of separation of electric charge (voltage) • Chemical potential energy – Energy contained within chemical bonds • Nuclear potential energy – Energy contained within the nucleus

  6. Heat • Heat is the transfer of thermal energy either to or from a system. • Heat is given the symbol, Q. • Positive heat transfers heat to a system. (Endothermic process) • Temperature of substance increases • Negative heat releases heat to the surroundings. (Exothermic process) • Temperature of substance decreases • Each substance absorbs/releases at a characteristic rate called it’s heat capacity. A substance with a high heat capacity requires a large amount of energy to change its temperature.

  7. Initial state Final state Endothermic process • An endothermic process is one that absorbs heat. • You must heat an endothermic process to make it occur. • Energy is a reactant. • Q, heat is positive • The system gets hotter. • Surroundings gets colder. • T = Tfinal– Tinitialis positive Tf > Ti E Energy

  8. Energy Initial state E Final state Exothermic process • An exothermic process is one that releases heat. • An explosion is an exothermic process (easy way to remember) • Energy is a product. • Q, heat is negative • The system gets colder. • Surroundings gets hotter. • T = Tfinal– Tinitialis negative Tf< Ti

  9. Specific heat capacity, c • If the heat capacity is per gram of material, it is the specific heat capacity, c. • Specific heat capacity is the amount of energy needed to raise the temperature of 1 gram of substance by 1 degree Celsius. Typical units are cal/g◦C or J/gK. • ◦C and K are interchangeable for these units. • Problems may use either Joules or calories. • Given a choice, use Joules form. • Note water’s extremely high value • 1 Food Calorie = 1 kcal (note the capital C)

  10. Measuring heat, q • For any change in temperature from Tinitial to Tfinal, ΔT = Tfinal – Tinitial • For a temperature increase, ΔT is positive. • For a temperature decrease, ΔT is negative. • Heat exchanged during the temperature change is given by: • Where q is the heat, m is the mass of the substance, c is the specific heat capacity of the substance and ΔT is the temperature change.

  11. Heat calculations • Ex: How much heat is needed to raise 2.50 g of water from 25 ◦C to body temperature of 37 ◦C? • What mass of aluminum can be heated from 5°C to 45°C by using 275 J of heat? (Specific heat capacity of Al = 0.900 J/g°C)? • What is the final temperature when 36.4 J of of heat is lost from a 23.8 g piece of lead initially at 85°C? (Specific heat capacity of Pb= 0.128 J/g°C)? q = m = c = ΔT =

  12. Heating Curve of Water • Heat and temperature are not the same. • Phase changes occur at a constant temperature, but still require heat to happen. • Not all phase changes require the same amount of heat • It takes more energy to boil than to melt. • It takes more heat to warm water than ice or steam the same amount. • The slopes of the ice and steam lines are greater than the line for water.

  13. Exit Slip - Homework • Exit Slip: How much heat is needed to warm a 450 g copper pan from 25°C to 150°C ? (Use joules) • What’s Due? (Pending assignments to complete.) • Heat Worksheet • What’s Next? (How to prepare for the next day) • Start reviewing for Test 2 Oct 31

More Related