Calculate the quantity of heat required to raise the temperature of 400 cm³ of water from 25 °C to 80 °C.
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Question No. 2
An immersion heater rated at 140 W is used to melt 100 g of crushed ice and raise the temperature of the melted ice to 10 °C. Determine the time taken for this process, assuming there is no heat loss.
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Question No. 3
Francisca and Ayodele conducted an experiment to determine the specific heat capacity of water, using a hot block of copper and a copper calorimeter with water. They recorded: Mass of calorimeter = 53.6 g; Mass of calorimeter + water = 92.5 g; Mass of hot copper + calorimeter + water = 140.8 g; Initial temperature of water = 15.9 °C; Temperature of hot copper = 93.3 °C; Final temperature of water and copper = 23.2 °C.
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Question No. 4
In an experiment to measure the specific latent heat of vaporisation of water, cold water was placed in an insulated copper calorimeter and dry steam was added. Data recorded: Mass of calorimeter = 50.5 g; Mass of calorimeter + water = 91.2 g; Temperature of steam = 100 °C; Mass of calorimeter + water + steam = 92.3 g; Final temperature of water = 25 °C.
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Question No. 5
Evaporation of sweat from the human body is an important method of keeping the body cool in hot weather. Determine the mass of sweat that must evaporate from the surface of a 70 kg man in order to cool him by 1 °C. Take L_v = 2.42 × 10⁶ J kg⁻¹ and c = 4 200 J kg⁻¹ °C⁻¹.
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Question No. 6
Give two methods of (a) increasing the boiling point of water and (b) decreasing the melting point of water.
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Question No. 7
A small refrigerator freezer has a power rating of 100 W and is 80% efficient.
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Question No. 8
Allowing a liquid to evaporate in a closed pipe inside the freezer cools the air in the freezer. The vapour is then pumped through the pipe to the outside of the freezer, where it condenses again.
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Question No. 9
The hottest month in the city of Kano is April, when the average daily maximum temperature is 38 °C. If the relative humidity for April is 36% and the saturation vapour pressure is 6.63 kPa, determine the actual vapour pressure.
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Question No. 10
A skin burn caused by steam at 100 °C is much worse than that caused by water at 100 °C. By calculating the quantity of heat given off by (a) 10 g of steam at 100 °C cooling to skin temperature at 34 °C, and (b) 10 g of water at 100 °C cooling to 34 °C, prove the above statement.
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Question No. 11
The specific latent heat of vaporisation is the quantity of heat required to change:
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Question No. 12
Equal quantities of heat are given to copper, lead, aluminium and iron, all of them having the same mass and all initially at room temperature. If no change in state occurs, which of the metals will have the largest final temperature?
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Question No. 13
When a gas changes state to a liquid, the temperature is:
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Question No. 14
The latent heat of fusion of the substance is:
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Question No. 15
The quantity of heat required to change 1 kg of a substance by 1 °C is called:
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Question No. 16
When 2 kg of water freezes to form ice:
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Question No. 17
Iodine sublimes because it changes from:
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Question No. 18
The temperature at which the water vapour in the air becomes saturated and condenses on the ground is known as:
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Question No. 19
The condensation point of the substance is:
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Question No. 20
Which one of the following statements about evaporation is INCORRECT?
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