Unit 6 Review
Kinetics and Thermochemistry
Wednesday 5/4
Have phase diagram hw out right away
please
AFTER SCHOOL REVIEW WILL BE AWESOME! IT IS ALSO
ON THE WEB FOR THOSE OF YOU WHO CAN’T MAKE IT.
PLEASE COME! 2:20 – 3:15. 5 EXTRA CREDIT POINTS. AND
EXTENSION ON LAST NIGHTS HW.
Unit 6 Review
Kinetics and Thermochemistry
Please take out paper to complete today’s review. Your
notes may also be helpful.
Each part of today’s in class review is worth points.
Please number each slide and complete each section.
You will have a limited amount of time for each section.
Please keep up.
1 - Specific Heat
What mass of magnesium is present if 250 J
raises the temperature from 25 °C to 27 °C?
Specific heat 1.02 J/gK
What is the heat capacity of an unknown
metal if 65.5 grams absorbs 1550 J and
undergoes a temperature change of 62.0 C°?
1 - Specific Heat Answers
What mass of magnesium is present if 250 J
raises the temperature from 25 °C to 27 °C?
Specific heat 1.02 J/g °C
◦ m= 250 J/(1.02 J/g °C x 2 °C) = 122.5 g = 120 g
What is the heat capacity of an unknown metal if
65.5 grams absorbs 1550 J and undergoes a
temperature change of 62.0 C°?
◦ Cp = 1550J / (65.5 g x 62.0 °C) = 0.382 J/g °C
2 - Calculation of Energy
How many joules are required to melt 650
grams of water?
How many joules are required to boil 650
grams of water? Substance Specific Heat (J/g◦C)
H2O (l) 4.184
H2O (steam) 2.02
Water
Heat of fusion = 334 J/g
Heat of vaporization = 2260 J/g
Substance
H2O (l)
Specific Heat (J/g◦C)
4.184
2 - Calculation of
H2O (steam) 2.02 Energy Answers
Water
Heat of fusion = 334 J/g
Heat of vaporization = 2260 J/g
How many joules are required to melt 650 grams of
water?
◦ Hfusion = 334 J/g x 650 g = 217,100 J = 220,000 J
How many joules are required to boil 650 grams of
water?
◦ H vap = 2260 J/g x 650 g = 1,469,000 J = 1,500,000J
1. Going from a solid to a gas is an
3- Heat Curve… (exothermic, endothermic) process
because energy is (absorbed, released).
4. Why does sweating help cool you off?
2. During phase changes the temperature
(increases, decreases, remains constant).
3. List the states of matter in order of
increasing kinetic energy.
3- Heat Curve Answers
1. Going from a solid to a gas is an
4. Why does sweating help cool you off? (exothermic, endothermic) process
Sweating happens when water molecules because energy is (absorbed, released).
evaporate (vaporize) from liquid droplets
on your arm to gas. When these high
energy molecules escape they lower the
overall kinetic energy of the remaining
molecules – lowering your body
temperature as a result!
2. During phase changes the temperature
(increases, decreases, remains constant).
3. List the states of matter in order of
increasing kinetic energy.
Solid to liquid to gas
4- Phase Change Diagrams
Which line represents
the freezing point?
Which line represents
the boiling point?
Describe what happens
a the triple point?
Describe what happens
at the critical point?
4 - Phase Change Diagrams Answers
Which line represents the freezing
point? (fusion line)
Which line represents the boiling
point? (vaporization line)
Describe what happens a the triple
point? (all 3 states exist
simultaneously)
Describe what happens at the
critical point? (the liquid state
can no longer exist at these
extremely high temps – no
matter the pressure)
5 - Phase Change Diagram
1. How could you directly
change “Q” to a solid? Q
2. Identify two ways you
could change “Q” to a
gas. Be specific.
3. Describe CLEARLY
what is happening when
A becomes A’.
4. Describe CLEARLY
what is happening when
B becomes B’.
5 - Phase Change Diagram Answers
1. How could you directly change “Q” to a
solid? Q
2. Decrease temp at same pressure.
3. Identify two ways you could change “Q” to
a gas. Be specific.
4. Raise temp at same pressure. OR, lower
pressure at same temp.
5. Describe CLEARLY what is happening
when A becomes A’.
6. Pressure held constant. Solid A heated,
solid A melts at MO, liquid A is heated,
liquid A vaporizes at PO, gaseous A is
heated to A’.
7. Describe CLEARLY what is happening
when B becomes B’.
8. Pressure held constant. Solid B is heated,
solid B sublimates at SO, gaseous B is
heated to B’
6 - Potential Energy Diagrams
Draw an energy diagram:
Heat of reactants: 4.5 KJ
Heat of products: 10.5 KJ
Energy of activated complex: 15 KJ
Heat of reaction: _____ KJ
Activation Energy: ______ KJ
Exothermic/Endothermic?
How does a catalyst affect this graph?
6 - Potential Energy Diagrams Answers
Draw an energy diagram:
Heat of reactants: 4.5 KJ
Heat of products: 10.5 KJ
Energy of activated complex: 15 KJ
Heat of reaction: _____ KJ (10.5 – 4.5 = 6 KJ)
Activation Energy: ______ KJ (15 – 4.5 = 10.5 KJ)
Exothermic/Endothermic? ENDOTHERMIC (Products higher
than reactants)
How does a catalyst affect this graph? (lowers the
activation energy so faster reaction)
7 - Potential Energy Diagrams
Draw an energy diagram:
Heat of reactants: 250 KJ
Heat of products: 25 KJ
Energy of activated complex: 350 KJ
Heat of reaction: _____ KJ
Activation Energy: ______ KJ
Exothermic/Endothermic?
How does a catalyst affect this graph?
7 - Potential Energy Diagrams
Answers
Draw an energy diagram:
Heat of reactants: 250 KJ
Heat of products: 25 KJ
Energy of activated complex: 350 KJ
Heat of reaction: _____ KJ (25 – 250 = -225 KJ)
Activation Energy: ______ KJ (350 – 250 = 100 KJ)
Exothermic/Endothermic? EXOTHERMIC, energy of
products is LESS than reactants so excess energy given off!
How does a catalyst affect this graph? Again, catalyst lowers
the activation energy
8 - Collision Theory
Identify 5 ways to increase the rate of a
reaction.
8 - Collision Theory Answers
Identify 5 ways to increase the rate of a
reaction.
Increase temp – more collisions
Increase concentration of reactants –
more collisions
Increase Pressure
Decrease volume
Add a catalyst
Add a more reactive substance
9- Reaction Rate
Calculate the rate of the reaction below.
Time (second)
9- Reaction Rate Answers
Calculate the rate of the reaction below.
Rate = change in something/change in time
= (135 nm – 0 nm)/100 sec
= 1.35 nm/sec
Time (second)