2.2.2 Specific heat capacity (3)
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1.
A solid block of iron initially has a temperature of 20°C. It is heated using a heater and its temperature increases to 80°C. Explain, using the kinetic theory of matter, what happens to the average kinetic energy of the iron atoms during this process. Also, describe how this change in average kinetic energy relates to the observed change in the material's temperature.
When the iron block is heated from 20°C to 80°C, the average kinetic energy of the iron atoms increases. This is because the heater provides energy to the atoms, causing them to vibrate with greater amplitude and move with higher speeds. The kinetic theory states that the average kinetic energy of the atoms is directly proportional to the absolute temperature. Therefore, as the temperature increases, the average kinetic energy of the atoms also increases.
The observed change in the material's temperature is a direct consequence of this increase in average kinetic energy. Temperature is a macroscopic measure of the average kinetic energy of the particles within a substance. The higher the average kinetic energy of the iron atoms, the higher the temperature of the iron block. The increased kinetic energy allows the atoms to overcome their intermolecular forces more readily, leading to expansion and the perceived increase in temperature.
2.
A laboratory technician measures the following data for a sample of water: m = 250 g, Δθ = 15°C. Calculate the energy required to raise the temperature of the water by 15°C. The specific heat capacity of water is 4.18 J/g°C. Show your working.
Equation: c = ΔE / m Δθ
Given:
- m = 250 g
- Δθ = 15°C
- c = 4.18 J/g°C
To find: ΔE
Rearranging the equation to solve for ΔE: ΔE = c * m * Δθ
Substituting the values: ΔE = 4.18 J/g°C * 250 g * 15°C
Calculation: ΔE = 4.18 * 250 * 15 = 15675 J
Answer: The energy required to raise the temperature of the water by 15°C is 15675 J.
3.
Define specific heat capacity in terms of the energy required and the resulting temperature change. Explain its significance in everyday applications, giving two examples.
Definition: Specific heat capacity (c) is defined as the amount of energy (ΔE) required to raise the temperature of a unit mass (m) of a substance by one degree Celsius (Δθ). Mathematically, it is expressed as c = ΔE / m Δθ.
Significance in everyday applications: Specific heat capacity is a crucial property of materials that influences how they respond to changes in temperature. Substances with high specific heat capacities require a lot of energy to change their temperature, while those with low specific heat capacities change temperature more easily.
Examples:
- Water as a coolant: Water has a high specific heat capacity (approximately 4.18 J/g°C). This means it can absorb a large amount of heat without a significant temperature increase. This makes it an excellent coolant in engines and other systems.
- Metals in cooking pots: Metals have relatively low specific heat capacities. This means they heat up quickly when placed on a stove. This allows for efficient and rapid cooking.