1. The Driving Forces Exothermic & Endothermic Entropy
Chapter 2
The Driving Forces
Exothermic & Endothermic Entropy

2. All changes whether physical or chemical involve a change in energy.
It can be released during the change (exothermic).
It can be absorbed during the change (endothermic).
The amount of energy that is released or absorbed in measured in joules (J) or calories (cal).

5. Energy Change and Bond Breakage/Formation
Bonds are energy.
Each different type of bond has an amount of energy associated with it.
When we break a bond the process requires energy (it is endothermic).
When we form a bond the process releases energy (it is exothermic).
The net energy change determines whether the reaction is endothermic or exothermic.
Example: I break one bond and form two. Overall, the reaction is exothermic!

6. Energy Change and Bond Breakage/Formation
NH4NO3 → NH4+ + NO3-
Here we broke the bond holding the two ions together through mixing with water. That broken bond results in an endothermic reaction because it took energy to break that bond.

7. Mg + HCl MgCl2 + H2

8. Energy Change and Bond Breakage/Formation
If we don’t know how to write the reaction, we can often determine whether energy is being released or absorbed by determining if any temperature change occurs.

9. Temperature Change Exothermic reactions “often” feel hot.
Endothermic reactions “often” feel cold.

11. Spontaneous vs. Nonspontaneous
A spontaneous process is a process that occurs without outside intervention.
No external forces are required to keep the process going, although external forces may be required to get the process started.

12. Activation Energy
The activation energy is the amount of energy that must be added to a reaction for it to occur.
Both exothermic and endothermic reactions require activation energy.

15. Spontaneous vs. Non-spontaneous
A non-spontaneous process will not occur naturally.

16. The Driving Forces
All reactions (changes) in nature occur because of the interplay of two driving forces:
(1) The drive toward lower energy.
(2) The drive toward increased randomness (entropy).

17. Entropy
Some call it entropy. I call it heaven
Entropy is the amount of randomness (lack of order) in a system.

18. Entropy
Entropy is how “chaotic”, (disordered), a system is.

19. Increase in Entropy
Entropy can be increased as long as more chaos has been created. This can be done in five main ways.
Producing a liquid from a solid
Producing a gas from a solid
Producing a gas from a liquid
Forming a mixture
Creating more particles

20. Increase in Entropy
Production of liquid or gas from a solid.

21. Increase in Entropy
Production of gas from a liquid.

22. Entropy

23. Increase in Entropy
Formation of a mixture.

24. Increase in Entropy
More particles are created.

25. As a reaction Releases Energy
The reaction causes an Increase in Entropy

26. Specific Heat
When a physical or chemical change occurs, it is associated with an energy change. We can measure the amount of energy lost or gained through a system by using an equation:
Q=mc t

27. Q=mc t
Q = energy absorbed/released (Joules/Calories) m = mass (grams) c = specific heat; the amount of energy needed to raise the temperature of an object that is one gram by 1 °C. (J/g°C) t = change in temperature; Tbigger-Tsmaller(°C)

28. 1. ) When 3. 0 kg of water is cooled from 80. 0 degrees Celsius to 10
1.) When 3.0 kg of water is cooled from 80.0 degrees Celsius to 10.0 degrees Celsius, how much heat energy is lost?

29. 2.) 2.52 x 104 J of heat are added to 2.0 kg of mercury to reach a final temperature of 130 degrees Celsius. What was the initial temperature of the mercury?

30. mc t=mc t Energy Exchange
So far, the problems we have used to calculate specific heat only look at one of the items losing or gaining energy. We can also look at how energy is exchanged between the two items in the process by setting up the equation in this way:
mc t=mc t

31. Energy Exchange
We know that energy lost by one object will be gained by the other in the system (Law of Conservation of Energy). Because of this, we can equal the energy lost by one object to the energy gained by the other. The set up and units are the same! Remember, the bigger temperature will go first, and the smaller temperature last!

32. 3. ) 0. 100 kg of an unknown metal at 94ºC is placed in 100
3.) kg of an unknown metal at 94ºC is placed in 100. grams of water at 10.ºC. The final temperature of the metal and water are 17ºC. What is the heat capacity of the unknown metal?

33. 4.) Carbon has the highest melting point (3620 degrees Celsius) of an element and a specific heat of J/gC. Tungsten has a specific heat of J/gC. An 11.2g sample of carbon is heated to its melting point and allowed to radiate heat to a piece of tungsten. The tungsten has an initial temperature of 31.0 degrees Celsius. The final temperature of both is 990 degrees Celsius. What was the mass of the tungsten sample?