The rate at which an object cools (i.e. how quickly its temperature decreases) depends upon several factors, including:
- Surface area
- Type of insulation
- Temperature difference with the surroundings
For this investigation, the effect of the temperature of water upon the rate of cooling will be investigated. The temperature-drop over 5 minutes (600 seconds) will be measured for 200ml of water at different start temperatures. The average rate of cooling can then be found by:
- digital stopwatch
- 250ml beaker
- rubber bung
- bunsen burner
- retort stand and clamp
- Volume of water used: 150ml
- Size of beaker (i.e. constant surface area): 250ml
- Time interval of cooling: 5.0 minutes (600 seconds)
- Temperature of the room: 21°C
- Fill an empty beaker with exactly 150ml of water (check side-scale of beaker)
- Set up apparatus as shown above. Ensure the thermometer is about 2cm above the bottom of the beaker.
- Light the bunsen burner and put on a blue flame. Heat up the water.
- When the temperature on the thermometer has reached 90°C, immediately switch off the burner.
- Start the stopwatch and time for 5.0 minutes.
- Read the thermometer value at the 5.0 minute mark.
- Before repeating the experiment, check the level of water is still 150ml (some may have evaporated) and add more water if required.
- For different start temperatures, repeat steps 3-7 but turn off the burner at the desired temperature.
|Start Temperature of Water (°C)||Temperature after 5min (°C)||Drop in Temperature|
|Average Rate of Cooling x 1000 (°C/s)|
There is a strong correlation between the average rate of cooling and the start temperature: the greater the start temperature, the faster the average rate of cooling.