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In an experiment to measure the specific latent heat of vaporisation of water, cool water was placed in an insulated copper calorimeter - Leaving Cert Physics - Question 2 - 2005
Question 2
In an experiment to measure the specific latent heat of vaporisation of water, cool water was placed in an insulated copper calorimeter. The following data was recor... show full transcript
Worked Solution & Example Answer:In an experiment to measure the specific latent heat of vaporisation of water, cool water was placed in an insulated copper calorimeter - Leaving Cert Physics - Question 2 - 2005
Step 1
Calculate a value for the specific latent heat of vaporisation of water.
Answer
To determine the specific latent heat of vaporisation of water, we follow these steps:
-
Calculate the mass of water (m_w):
m_w = Mass of calorimeter + water - Mass of calorimeter
m_w = 91.2 g - 50.5 g = 40.7 g = 0.0407 kg
-
Calculate the temperature change (Δθ):
- The initial temperature of water is 10 °C and the final temperature is 25 °C.
Δθ = Final temperature - Initial temperature
Δθ = 25 °C - 10 °C = 15 °C
-
Calculate the heat gained by water (Q_w):
Using the formula:
Q_w = m_w imes c_w imes Δθ
where:
- c_w = specific heat capacity of water = 4200 J kg⁻¹ K⁻¹
Q_w = 0.0407 kg imes 4200 J kg⁻¹ K⁻¹ imes 15 K
Q_w = 2561.4 J
-
Calculate the mass of steam (m_s):
m_s = Mass of calorimeter + water + steam - Mass of calorimeter - mass of water
m_s = 92.3 g - 91.2 g = 1.1 g = 0.0011 kg.
-
Calculate the specific latent heat (L):
The specific latent heat of vaporisation can be found using the equation:
Q = m_s imes L ightarrow L = \frac{Q}{m_s}
Rearranging gives:
L = \frac{2561.4 J}{0.0011 kg}
L = 23285.45 J kg⁻¹
Thus, the specific latent heat of vaporisation of water is approximately 22830 J kg⁻¹.
Step 2
Why was dry steam used?
Answer
Dry steam was used because condensed steam would have already lost some heat to the surrounding environment, making it less effective in providing the necessary energy to raise the temperature of the water. Using dry steam ensures that all heat energy is transferred directly to the cooler water, allowing for a more accurate measurement of the specific latent heat of vaporisation.
Step 3
Step 4
A thermometer with a low heat capacity was used to ensure accuracy. Explain why.
Answer
A thermometer with a low heat capacity is used because it absorbs less heat than a heavier thermometer. This allows for a more precise measurement of temperature changes, as the thermometer will not significantly alter the amount of energy being measured in the system. This minimizes any heat loss or gain, leading to more accurate results.