Chemistry – U3 Review 2013Due Monday, 12/2

NOTE: the completed review WS must be turned in at the beginning of class on 12/2….no exceptions!

If you will not be at school, do one of the following:

have a friend or sibling hand WS in

scan WS and email to me

fax WS to me at school(740) 363-9380

take picture of each page and email to me

To prepare for the U3 test, assemble your notes, worksheets and quizzes and review them with the

unit learning targets as your guide. Working in a small group where you can draw from each other’s

understanding can help you prepare thoroughly.

Energy

Think of energy as a quantity that is always involved when there is a change in the state of matter.

When a substance gets hotter or colder or changes phase, energy is either transferred into or out

of the system. The two key ways energy is stored is kinetic (due to the motion of the particles) and

interaction (due to attractions between the particles). Remember that attractions lower the energy

state, so one must add energy to a system to pull particles apart. The three ways that energy is

transferred is by heating (Q), working (W) and radiating (R); this course focuses on Q. You will be

expected to be able todraw energy bar graphs to account for energy storage and transfer in all

sorts of changes.(review ws 1 and 2 and quiz)

  1. Make up 2 sample situations (one that involves a phase change and one that does not) and sketch the bar graph.

A.

B.

Kinetic Molecular Theory

This theory describes all matter as being composed of tiny particles in endless random motion. In a

solid, the particles vibrate, but are locked into an orderly array. In a liquid, the particles are still

touching but are free to move around past one another. In a gas, the particles are moving very

rapidly and are widely separated.

When energy is transferred to a sample of matter, either the particles speed up (temperature

increases) or they get pulled apart (phase change), but not both at the same time. This helps

account for the shape of the warming curve you got in the Icy Hot lab.

  1. Draw a heating curve for water (half page of graph paper). Begin at -5oC and end at 105oC. Remember, water always has the same plateaus at the same temperatures! Label them!
  • Mark on your graph for each section:

the phase(s) present

into which account (EK or EPH) is energy being added

  • On your graph, identify where the following phases or changes occur. Mark a point on the graph and label it with the corresponding letter.
  1. Some of the solid water has melted…you see both solid and liquid
  2. A solid at 0oC.
  3. Some liquid and some gas is seen……boiling!
  4. A liquid at 25oC
  5. Pure gas
  6. A liquid at 100oC
  7. A gas at 100oC
  8. Pure solid
  9. A liquid at 0oC
  1. Draw a cooling curve for water on the other half of the graph paper. Remember, water always has the same plateaus at the same temperatures! Label them on this graph also.

Mark on your graph for each section:

the phase(s) present

b. from which account (EK or EPH) is energy being taken away

  1. How are heat and temperature different?
  1. True or False. If you don’t stir a liquid or a gas, the particles are not moving. Explain yourreasoning.

6. Which contains more thermal energy, an iceberg or a liter of hot water? Explain.

  1. What is happening to temperature while ice is melting to become (liquid) water? Explain.
  1. What specifically is inside a bubble in boiling water? Where did this come from?

Quantitative Energy calculations

When the temperature of a solid, liquid or gas is changing, energy, in the form of heat, Q, is involved. Rather than simply plug-n-chug values into an equation, reason out the quantity of Q from the value of c. For example, you know that 4.18 J is required to increase the temperature of each gram of liquid water by one Celsius degree. If you have more than one gram of water, or if the temperature changes by more than one degree, multiply by the appropriate amounts.

When the substance is undergoing a phase change (freezing or melting, condensing or evaporating), you know that you must use either Hf or Hv, both of which are factors that tell us the quantity of heat, Q involved for each gram. If more than one change is taking place, you must break the problem into steps. For these situations, temp-time graphs help you decide what is involved in each step (review ws 3 and 4).

First, before you do any math, you should sketch a temperature-time curve so that you can focus on

what changes are taking place.

9.On the graphs below sketch and label the curve that describes each “story”:

AB

Initial state: 150 g solid water at –10 ˚CInitial state: 200 g liquid water at 40 ˚C

Final state: 150 g liquid water at 0˚C Final state: half of the water has boiled away at 100˚C

Energy constants (H2O)

334 J/g Heat of fusion (melting or freezing) Hf

2260 J/gHeat of vaporization (evaporating or condensing) Hv

2.1 J/g˚CHeat capacity (c) of solid water

4.18 J/g˚CHeat capacity (c) of liquid water

10.Calculate the heat required to bring about the change in #9A. (2 steps)

11. Calculate the heat required to bring about the change in #9B. (2 steps)

12. How much heat is necessary to change a 64.0 g sample of water at 35.0 °C into

steam at 108.0 °C? (3 steps)

Modeling Chemistry1U3 review v2.2