04.04.24 - Entropy

✍️Aim: Why do some reactions occur spontaneously?

Poll

How are you feeling today?

• Good

• Okay.

• Tired

• Can we chat?

Do Now: 4 Questions

Multiple Choice

1.  What is the value PE of the reactants?

• 240 kJ

• 160 kJ

• 80 kJ

• 120 kJ

Multiple Choice

2.  What is the value PE of the products?

• 240 kJ

• 160 kJ

• 80 kJ

• 120 kJ

Multiple Choice

3.  What is the value Activation Energy of the reaction?

• 240 kJ

• 160 kJ

• 80 kJ

• 120 kJ

Multiple Choice

4.   Based on the information in the diagram and your prior answers to questions 1 and 2, what is the enthalpy ∆ H of the forward reaction? Calculate it.

• 240 kJ

• 160 kJ

• 80 kJ

• 120 kJ

✍️Why do reactions happen spontaneously?

• Heat = H

  • change in heat =ΔH

  • ΔH = Enthalpy

• Entropy (S): the change in disorder/randomness of particles

  • change in entropy = ΔS

• Spontaneous Reactions: any reaction that will occur naturally by itself.

• When do reactions happen spontaneously?

  • heat (ΔH) decreases (-)

  • entropy (ΔS) increases (+)

Let's Practice!

Multiple Choice

5. What is the definition of enthalpy?

• measure of disorder

• change in heat and energy

• change in moles

• measure of volume

Multiple Choice

6. Look at Table I.  Are most reactions endothermic or exothermic?

• Exothermic

• Endothermic

• Neither

Multiple Choice

7. What is the definition of entropy?

• measure of disorder

• change in heat and energy

• change in moles

• measure of volume

Multiple Choice

8. Which physical phase has the highest entropy?

• Solid

• Liquid

• Gas

• Aqueous