The specific latent heat of fusion of ethyl alcohol is 100 Jg -1 . Find the heat absorbed (in J) by 2.25 g of ethyl alcohol when it melts at its melting point of -114°C.
Understanding Heat Absorption During Melting
When a substance melts, it absorbs energy without changing its temperature. This energy is used to break the bonds holding the particles in the solid state. The amount of energy required for a unit mass of a substance to melt at its melting point is called its specific latent heat of fusion.
Applying Specific Latent Heat of Fusion
The question provides the specific latent heat of fusion for ethyl alcohol and the mass of ethyl alcohol that melts. We need to find the total heat absorbed by the ethyl alcohol during this phase change (melting).
- Given: Specific latent heat of fusion (\(L_f\)) of ethyl alcohol = \(100 \text{ Jg}^{-1}\)
- Given: Mass (\(m\)) of ethyl alcohol = \(2.25 \text{ g}\)
- The melting point (\(-114^{\circ}\text{C}\)) is given, but it's the temperature at which melting occurs, not needed for the calculation of heat absorbed during the phase change itself.
The formula to calculate the heat absorbed (\(Q\)) during melting is:
\(Q = m \times L_f\)
Step-by-Step Calculation of Heat Absorbed
Substitute the given values into the formula:
\(Q = 2.25 \text{ g} \times 100 \text{ Jg}^{-1}\)
\(Q = 225 \text{ J}\)
Therefore, the heat absorbed by 2.25 g of ethyl alcohol when it melts at its melting point is 225 Joules.
Result Summary
The calculation shows that 225 J of heat is absorbed by the ethyl alcohol during the melting process.
| Quantity | Value | Unit |
|---|---|---|
| Specific Latent Heat of Fusion (\(L_f\)) | 100 | J/g |
| Mass (\(m\)) | 2.25 | g |
| Heat Absorbed (\(Q\)) | 225 | J |
Revision Table: Key Concepts
| Concept | Definition | Formula |
|---|---|---|
| Latent Heat | Heat energy absorbed or released during a phase transition (like melting, freezing, boiling, condensation) at constant temperature. | N/A |
| Specific Latent Heat of Fusion (\(L_f\)) | Heat energy absorbed per unit mass of a substance to change it from solid to liquid state at its melting point. | \(L_f = Q/m\) |
| Heat Absorbed During Melting (\(Q\)) | Total heat energy required to melt a given mass of a substance at its melting point. | \(Q = m \times L_f\) |
Additional Information: Phase Changes and Energy
Phase changes, such as melting, freezing, boiling, condensation, sublimation, and deposition, involve the transfer of energy.
- Melting (Solid to Liquid): Energy is absorbed (endothermic). The substance absorbs heat equal to \(m \times L_f\).
- Freezing (Liquid to Solid): Energy is released (exothermic). The substance releases heat equal to \(m \times L_f\).
- Boiling (Liquid to Gas): Energy is absorbed (endothermic). This involves the specific latent heat of vaporization (\(L_v\)), and heat absorbed is \(m \times L_v\).
- Condensation (Gas to Liquid): Energy is released (exothermic). The heat released is \(m \times L_v\).
During a phase change, the temperature of the substance remains constant as the absorbed or released energy is used to change the state rather than increase or decrease kinetic energy of particles.
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