18.10
Calorimetry
When objects at different temperatures are placed in contact with each other but isolated from everything else, they attain thermal equilibrium. A con…
Calorimetry is the science of measuring the heat released and absorbed during a physical or chemical process under restricted conditions.
The principle of calorimetry implies that if two bodies are isolated from the surroundings, the heat gained by the cold body is equal to the heat loss by the hot body, i.e., their sum is equal to zero.
If 30 grams of ice cubes at zero degree celsius are dissolved in 150 grams of orange juice at 40 degree celsius, what would be the final temperature of the liquid after all the ice is melted? The specific heat of juice and ice is 4190 J/kg.K and 2100 J/kg.K, respectively, and the heat of fusion of ice is 334x103 J/kg.
First, list the known and unknown quantities.
Now apply the principle of calorimetry to juice and ice.
Rearrange the terms to find an expression for final temperature.
Substitute the values to calculate the final temperature of the orange juice, which is 21.86 degree celsius.
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Q1: What is the basic principle of calorimetry?
Calorimetry is based on the principle of energy conservation: when two bodies at different temperatures are isolated from their surroundings, the heat gained by the colder body equals the heat lost by the hotter body. This ensures their combined heat change sums to zero. This principle applies whenever objects reach thermal equilibrium in an isolated system.
Q2: What is a calorimeter and how does it work?
A calorimeter is a container designed to prevent heat transfer between the system and surroundings. It isolates objects from external thermal influences, allowing accurate measurement of heat exchange between substances inside. The calorimeter enables precise determination of heat released or absorbed during physical or chemical processes by maintaining thermal isolation.
Q3: How do you solve a calorimetry problem involving phase changes?
To solve calorimetry problems with phase changes, identify known quantities including mass, specific heat capacity, and heat of fusion or vaporization. Apply the principle that heat lost equals heat gained. Account for energy required to change phase separately from sensible heat changes. Substitute values into the energy balance equation to find the final temperature or heat involved.
Q4: Why is thermal isolation important in calorimetry measurements?
Thermal isolation ensures that all heat exchange occurs only between the objects being studied, not with the environment. Without isolation, heat would transfer to or from surroundings, making measurements inaccurate. An insulated container or system prevents this external heat transfer, allowing the principle of heat conservation to apply correctly and yield reliable results.
Q5: What role does specific heat capacity play in calorimetry calculations?
Specific heat capacity determines how much energy is required to change an object's temperature by one degree. In calorimetry, it relates heat transferred to temperature change through the equation Q = mcΔT. Different materials have different specific heat capacities, so accounting for this property is essential for accurate calculations of heat flow and final equilibrium temperatures.
Q6: How does the orange juice and ice example demonstrate calorimetry principles?
In this example, cold ice absorbs heat from warm juice until both reach thermal equilibrium. The heat lost by juice equals the heat gained by ice, accounting for both temperature change and the energy required to melt the ice. By applying conservation of energy and using known specific heats and heat of fusion, the final equilibrium temperature can be calculated precisely.
Q7: What conditions must be met for a problem to be classified as a calorimetry problem?
A calorimetry problem requires that objects be thermally isolated from their surroundings, even if no explicit calorimeter container is mentioned. The system must prevent significant heat exchange with the environment during measurement. This isolation allows the heat gained by one object to equal the heat lost by another, enabling accurate application of energy conservation principles.