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*Lesson 7.3 : How much energy does it take to melt a glacier?                      

Review

  1. What did we learn last class about sea level rise? Complete the IMT for Lesson 2.

Water can change in volume by a lot because there's a lot of water in the ocean?

Part 1: What happens when heat is added to ice?

  1. In this lesson, we will investigate the energy it takes to melt a glacier. How would you model this process in the chemistry lab?  What supplies and materials would you need? 

$$ \begin{equation*}

q = m c \Delta T

,

c = heat

,

m = mass \end{equation*} $$

  1. In the boxes below,

  2. Draw and label models of 5 water molecules in the three states of matter:  solid, liquid, and gas. 

  3. Label the names of the processes between phases on the appropriate arrow.  Include vaporization, condensation, freezing, and melting

  4. List all of the phase change processes that involve the transfer of heat energy.

Solid => melting => Liquid => boiling => Gas
Solid <= freezing <= Liquid <= condensing <= Gas
  1. If the water molecules are the ‘system’, list the phase change processes that involve heat energy being transferred into or added to the system.

Melting

  1. If the water molecules are the ‘system’, list the phase change processes that involve heat energy being transferred out of or released from the system

Freezing

Investigation: What happens when heat is added to ice?

MATERIALS: 

  • 100-mL beaker

  • Crushed ice

  • Ice salt bath (NaCl + ice)

  • Thermometer

  • Ring Stand

  • Thermometer Clamp

  • Hot plate

  • Wooden disc

PRE-LAB: 

Read the lab procedures below and answer the following question.

  1. What will your graph look like? Circle the sketch that fits with your idea of what will happen.Hint: Time is the independent variable(x-axis), Temperature is the dependent variable (y axis)

8.  Why did you choose this graph?  How will it relate to your measurements? 

PROCEDURE:

  1. Before you begin, put on your goggles, and wear them properly throughout the investigation. 

  2. Mass a 100-mL beaker.  Record the mass in Data Table 1.

  3. Fill a 100 mL beaker about ⅔ full with crushed ice (from the orange container in the front of the classroom). Ice should be packed tightly into the beaker.

  4. Mass the 100-mL beaker with the crushed ice. Record the mass in Data Table 1. 

  5. Calculate and record the mass of the ice used in Data Table 1.

  6. Place the 100-mL beaker with the ice into the ice salt bath at your lab station, this will cool the contents of the beaker to below freezing. (Note: Add additional ice and/or salt to the ice salt bath if needed.)

  7. Place the thermometer into your 100-mL beaker with the ice. Wait until the temperature is  –2 °C or below. This will be your first reading (time will be 0 min) in Data Table 2. Also include observations in your data table. 

  8. After taking your first reading, remove your 100-mL beaker out of the salt-ice bath, placing the beaker on the wooden disc at your lab station. Continue to take measurements of time, temperature, and observation readings every minute for 5 minutes. 

  9. After 5 min, place the beaker on a hot plate. 

  10. Insert the thermometer into the metal clamp and place the thermometer mid-way into the beaker (see picture). The thermometer should not touch the sides or bottom of the beaker.

model|200

  1. Turn the hot plate on to a setting of 4-5; continue to record time, temperature, and observations every minute.

  2. The goal is to have the water boil. You may need to turn the hot plate to 8-9.

  3. Once contents in the beaker begin to boil, continue to make measurements for four minutes. Be careful not to boil all of the water from the beaker. 

  4. Remove the beaker from the hot plate, and place the beaker onto the wooden disc. Allow to cool. Turn off the hot plate.

  5. Clean up your lab area, return your goggles and apron. Wash your hands.

DATA TABLE 1: Mass of Ice
Mass of 100-mL Beaker 66.4
Mass of 100-mL Beaker + ice 140.42
Calculated Mass of ice 74.02

DATA TABLE 2: Heating of Water

DATA VISUALIZATION 

  1. Plot the time-temperature data for your investigation with time on the horizontal axis and temperature on the vertical axis.  Label your axes, and arrange the scales so the graph nearly fills the space available. 
Time (min) Temp (\(\textdegree C\))
1 -3
2 -3.5
3 -4
4 -4
5 -3
6 -2
7 -2
8 0
9 5.5
10 9
11 24
12 34
13 43
14 52
15 61
16 67
17 72
18 77
19 81.5
20 85
22 88
23 90
24 91
25 92
26 92
27 92
28 91
29 94
30 94
31 94.5
32 94.5
33 94
34 94
35 93
36 97
37 98
38 99
39 100
40 100
^temps 
type: line
id: temps
layout: cols
tension: 0.2
width: 100%
beginAtZero: false

HEATING CURVE OF WATER

energy of this phase change?

  1. Where is the energy going during the phase change?

into the particles, changing their kinetic energy and making them move faster

  1. What happens to the temperature of a substance as it undergoes a phase change?

the temperature drops a little as it starts to

  1. Why are phase changes considered physical changes?

the matter is changing from separate states of interaction. The phase of matter is a property of the mater

  1. Energy is being taken in by the system when the temperature rises from 40oC to 50oC.

  2. How are the molecules using this energy?

  3. What is the name given to this form of energy?

  4. Is thermal expansion occurring? Support your answer.

yes, because

  1. If a student measured the mass of water in the beaker at 70oC, it would be the same as the mass of ice at the beginning of the experiment.  Why is this so?

  2. If a student measured the volume of the water in the beaker at 70oC, it would not be the same as the volume of the ice at the beginning of the experiment.  Why is this so?

As you saw in the lab, the heating of ice is not linear.  Here is a link of a graph of what a phase change graph should look like.    The linked graph represents the overall phase changes of water. Moving up the diagram, you go from a solid to a gas (melting and then vaporizing). Moving from the top of the diagram back down, you go from a gas to a solid (condensation and then freezing)

The concept of the heating curve is very important as it helps us in figuring out what equation to use to quantify the heat associated with phase changes and temperature changes. We should note that two of the three things that could happen when you add heat to a substance is that either it will undergo a phase change, or its temperature will rise. These are the two effects being described by the heating/cooling curve. The mathematical equations are:

q=mc ΔT (energy of a temperature change within a phase)
q=ΔHm transition (energy of a phase transition)

It needs to be realized that if you add heat, you move to the right, and if you remove heat, you move to the left.

Let's use these two equations to quantify how much energy is needed for water to change temperatures.

  1. You have a sample of water which has a mass of 55.0g. How much energy does it take to heat water from -13 oC to 135 oC?

Because the temperature vs time graph is not linear it will help to find the amount of energy it takes for each section of the graph.  The total energy will be the sum total of all the energy from each section of the graph.

a. Heat the water from -13 °C to 0°C? 

b. Melt the ice?

c. Heat the water from 0°C to 100°C? 

d. Evaporate the water? 

e. Heat the water from 100°C to 135°C? 

f. Total heat needed.

  1. How many joules are added when 150.0g of water is heated from -20O C to 20O C?

  2. The average iceberg weight for the Grand Banks area is 150,000 tonnes.  (1 ton = 907.2 kg).  The average temperature of an iceberg is -15O C.  How much energy would it take to melt an iceberg from the Grand Banks area in kilojoules?

Last update: June 5, 2023
Created: June 5, 2023