Intro to chemistry

1. Intro to chemistry Therm o A. A graph of the temperature of the system versus the amount of heat added (or temp vs time if the heat is added at a constant rate) is called a ______ _____. heating curve

2. Intro to chemistry Therm o

3. Intro to chemistry Therm o A. We can calculate the energy change of the system for each of the segments of a heating curve using ________. In segments AB, CD, and EF we are heating a ______ phase from one temperature to another. Q=mCΔT single

4. Intro to chemistry Therm o 1. The ______ the specific heat of a substance, the more heat we must add to accomplish a certain temperature increase. higher

5. Intro to chemistry Therm o Example with H2O AB: 100. g • 2.10 J/gºC • 20.0ºC = 4,200 J

6. Intro to chemistry Therm o Example with H2O CD: 100. g • 4.18 J/gºC • 100.ºC = 41,800 J

7. Intro to chemistry Therm o Example with H2O EF: 100. • g 1.70 J/gºC • 25.0ºC = 4,250 J

8. Intro to chemistry Therm o A. In segments BC and DE we are converting one phase to another at a _________temperature. The temperature remains constant during these phase changes, because the added energy is used to overcome the attractive forces _________ molecules rather than to increase their average kinetic energy. constant between

9. Intro to chemistry Therm o 1. The energy required to make the solid to liquid transition is called the Heat of ______ (∆Hfus). For segment BC, in which ice is converted to water, the enthalpy change can be calculated by using ∆Hfus. fusion

10. Intro to chemistry Therm o 2. The energy required to make the liquid to gas transition is called the heat of ____________ (∆Hvap). For segment DE we can use ∆Hvap. vaporization

11. Intro to chemistry Therm o Q=n•∆Hfus or Q=n•∆Hvap (where n is number of moles)

12. Intro to chemistry Therm o Example with H2O BC: Q = (100 g • 1mole/18g) • (6.01 kJ/mole) = 33.4 kJ

13. Intro to chemistry Therm o Example with H2O DE: Q = (100 g • 1mole/18g) • (40.7 kJ/mole) = 226 kJ

14. Intro to chemistry Therm o a. There is no ∆T because during a phase change, the substance remains at a _______ temperature (the plateau on the graph) and no temperature change occurs. constant

15. Intro to chemistry Therm o b. These values are _____ to each particular substance and are measured in kJ/mole (or g/J). unique

16. Intro to chemistry Therm o A. The______ of the plateau is directly related to the amount of heat required to make the phase change. If more substance was making the phase change, the plateau would be _____. length longer

17. Intro to chemistry Therm o

18. Intro to chemistry Therm o B. Remember the angle of the sloping portion is directly related to the ______ ____ of the phase of the substance. specific heat

19. Intro to chemistry Therm o 1. The slope of the graph will be ______for substances with a lower specific heat. 2. The slope of the graph will be______ for substances with a higher specific heat. steeper gentler

20. Intro to chemistry Therm o C. Similar information can be portrayed in a ______ curve. cooling

21. Intro to chemistry Therm o A. Since temperature is a measure of ________ _______ _______, any change in temperature is a change in kinetic energy. All of the _________ line segments on a heating or cooling curve show a temperature change and therefore a change in kinetic energy. During these regions, a ______ state of matter exists and the sample is either getting hotter or cooler. average kinetic energy diagonal single

22. Intro to chemistry Therm o B. During the _________ line segments, there is ___ change in temperature, so kinetic energy remains constant. However, all the energy that is absorbed or released is related to changes in potential energy. horizontal NO

23. Intro to chemistry Therm o 1. Remember the 3 Ps: Plateau, Phase change, and Potential Energy Change.