Energy

1. Energy

2. What is energy? • Not matter, because it has no mass and does not occupy space • Ability to do work (work = moving an object a distance by a force)

3. What are the forms of energy? • Potential or kinetic • Potential – stored energy; energy an object has by virtue of its position • Kinetic energy – energy of motion

4. What are the forms of energy? • Electrical • Thermal • Light (electromagnetic) • Nuclear • Chemical • Mechanical • Gravitational

5. Energy is interconvertible • Potential ↔ Kinetic

6. Energy is interconvertible

7. Energy Forms • In chemistry, the forms of energy encountered the most are thermal and light. • Thermal energy is related to particle motion • Which has the highest thermal energy?

8. Energy Forms • Are heat and temperature the same? NO! • Heat = transfer of thermal energy based on temperature differences • Temperature = intrinsic property related to the hotness or coldness of an object; measures the effect of heat on an object; determines direction in which heat will be transferred

9. Heat Units • Calories – amount of heat required to raise one gram of water by 1oC nutritional calories – 1000 chemist calories or 1 kcal • Joule - equal to the work required to move a 1 kg mass against an opposing force of 1 newton1 J = 1 kg m2s-24.184 J = 1 cal • BTU (British thermal unit) – energy to raise 1 pound of water by 1oF

10. Temperature • Measured with a thermometer • Laboratory thermometers contains a liquid that expands as the liquid particles speed up. • Thermometers may work on the expansion of metals (thermostats). • Ear thermometers measure infrared energy and convert it to a temperature.

11. Temperature Scales What is a comfortable room temperature in oC? What is body temperature in oC?

12. Heat In and Out When we talk about energy transfer we need to define the “system” we are talking about. Surroundings Energy out = Exothermic SYSTEM Energy in = Endothermic Surroundings

13. Heat In and Out • When a system absorbs energy the process is endothermic. • When a system releases energy, the process is termed exothermic. • Of course, if a process is exothermic for the system, it is endothermic for the surroundings! • What do you think is preferred by a system- an endothermic or exothermic process?

14. Heat In and Out What processes involve energy? • Phase changes • Chemical changes • Dissolving • Heating or cooling a substance

15. Energy Conservation • Sometimes it appears that a process “loses” energy. However, the Law of Conservation of Energy says that energy cannot be created nor destroyed in a normal chemical process. So where does the energy go? • The system releases to or absorbs energy from its surroundings so it isn’t really lost.

16. How much energy is transferred? The amount of energy transferred to or from a system depends on three factors: • Amount of matter affected – the more matter, the more energy will be involved • Nature of the matter – different materials will absorb or release energy at different levels depending on their properties like particle forces and particle mass • Temperature change – the energy will depend on how much the particles change their motion

17. Specific Heat • Specific heat is the amount of energy required to raise one gram of a substance by 1oC. If you put an equal amount of heat into oil and copper, which one reach a higher temperature? Why?

18. Calculating Heat Exchange • How much energy is needed to change the temperature of 200 grams of water from 25oC to 40oC? Energy = sp.ht. x mass x ΔT Energy = 1.00 cal/g oC x 200 g x 15 oC Energy = 3000 cal or 3.0 kcal

19. Heat in Phase Changes • When a substance is boiling or freezing, does the temperature change? NO! • When phase changes occur, the energy lost or gained comes from the formation or breaking of forces between the particles • The amount of heat exchanged in the phase change depends on the heat of fusion (melting) and/or the heat of vaporization (boiling). The units are kcal/gram for each so the energy exchanged depends on the mass but not the temperature.

20. Cooling a gas…

21. Heating Curve

22. Chemical Changes and Electricity • You know that in some reactions there is an exchange of electrons (redox). If we design the system correctly we can tap the energy of these electrons as they move. • To generate energy the reactions have to be spontaneous.

23. Redox • CuSO4 + Fe -----> Cu + FeSO4 • Cu + AgNO3 Ag + Cu(NO3)2

24. Metal Plating • You can deposit layers of metal on a surface using an electrochemical reaction. This is a common industrial process. Copper plating on paperclips Deposition of silver (plating)

25. Batteries • Batteries used contained redox reactions to move electrons from a negative terminal or electrode to a positive terminal.

26. Batteries • Lead Storage battery used in vehicles

27. Dry and Wet Cell Batteries • When the electrolyte used to conduct the electrons has little moisture and/or is pasty, the battery is called a dry cell. • An auto battery which has liquid acid solution is called a wet cell.

28. Battery Life • When the chemical reaction in a battery stops, the battery “dies”. • If the chemical reaction used in the batteries is reversible, the battery can be recharged. Generally reactions that involve gases are not reversible. Exploded batteries

29. Chemical Changes and Electricity • We can also use flowing electrons to make a non-spontaneous reaction occur. Hydrolysis of water