Temperature-Time Graph During a Change of State


This practical lesson covers:

  1. How to obtain a temperature-time graph to show constant temperature during a change of state

Investigating the change in temperature during a change in state


Aim:

To obtain a temperature-time graph to show the constant temperature during a change of state of a substance.

Background information:

State changes, such as melting and boiling, occur at constant temperatures. During these transitions, adding heat does not increase the temperature until the state change is complete. In this practical, you will investigate the constant temperature during a state change using a temperature-time graph. By heating a substance like stearic acid or ice and recording the temperature at regular intervals, you can observe the plateau in the temperature curve when the substance changes state.

Variables:

  1. Independent variable - Material  
  2. Dependent variable - Temperature 
  3. Control variables - Heat source

Equipment:

  1. Heat source (e.g. hotplate or bunsen burner)
  2. thermometer
  3. beaker
  4. substance to investigate (e.g. stearic acid or ice)

Method:

  1. Fill a beaker with ice. 
  2. Insert the thermometer into the beaker of ice and place the beaker on the heating source. 
  3. Turn on the heating source to gradually heat the substance. 
  4. Measure and record the temperature at 30s intervals. 
  5. Once the substance reaches its melting point, continue to heat it until the change of state is complete. Continue taking temperature readings at 30s intervals. 
  6. Plot a graph of temperature (y axis) vs time (x axis).

During the melting process, the temperature of the ice-water mixture:

randomly fluctuates

remains the same

decreased

increases

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At what temperature will the ice begin to melt?

100 oC

0 oC

25 oC

1 oC

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How will the student know when all the ice has melted fully?

the temperature of the water will begin to increase

the water will begin to bubble

the temperature of the water will begin to decrease

the student won't be able to see ice in the water

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What type of graph should the student plot to show temperature vs time?

pie chart

bar chart

line graph

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