KULIAH TERMODINAMIKA BAB 3 BAGIAN 1 DENGAN JUDUL SIFAT ZAT MURNI

Summary

This lecture covers the fundamentals of thermodynamics in biosystems, focusing on the properties of pure substances, especially water (H2O). It explores the different phases of matter (solid, liquid, gas) and how to interpret phase diagrams and steam tables. Key topics include saturated liquid, latent heat, superheated vapor, and the process of phase transitions. The importance of understanding steam tables for future thermodynamic studies is emphasized. Practical applications such as vacuum frying technology are also discussed, demonstrating real-world uses of these thermodynamic principles.

Takeaways

• 😀 Zat murni (pure substances) have the same chemical composition in any phase (solid, liquid, gas). Examples include water and nitrogen.
• 😀 Water can exist in three phases: solid (ice), liquid (water), and gas (vapor), each maintaining the same chemical composition.
• 😀 The transition between phases, such as from liquid to gas, is fundamental in thermodynamics and is tracked using phase diagrams.
• 😀 The concept of saturated liquid refers to a liquid that is about to evaporate but hasn’t yet.
• 😀 Superheated vapor is defined as vapor at a temperature higher than its saturation temperature, even at the same pressure.
• 😀 The phase transition of water from liquid to vapor at 100°C is influenced by atmospheric pressure, and this relationship is illustrated in various thermodynamic diagrams.
• 😀 Saturation temperature and pressure are key concepts in determining when a substance changes phase from liquid to vapor.
• 😀 Latent heat refers to the energy required to change a substance’s phase without changing its temperature, for example, during vaporization or fusion.
• 😀 Evaporative cooling occurs when a liquid evaporates, absorbing energy and resulting in a cooling effect, even if the surrounding air is warmer.
• 😀 The critical point is where the liquid and vapor phases become indistinguishable, and it marks the highest temperature and pressure at which a substance can exist as both liquid and vapor.

Q & A

What is a pure substance in the context of thermodynamics?

A pure substance is defined as a substance that has the same chemical composition at all phases, whether in a solid, liquid, or gas state. Examples include water (H2O), which maintains the same composition across its different phases (solid, liquid, and gas).

Why is air considered a pure substance in thermodynamics?

Air is considered a pure substance because, despite being a mixture of gases, its composition remains consistent across different phases (solid, liquid, and gas). Therefore, it is treated as a single substance in thermodynamic calculations.

What is the significance of the steam table in thermodynamics?

The steam table is essential for determining the properties of a substance, such as water, at various temperatures and pressures. It provides data on saturation temperatures, pressures, specific volumes, enthalpies, and internal energy, which are crucial for solving thermodynamic problems, especially phase changes.

What is the meaning of a saturated liquid in thermodynamics?

A saturated liquid is a liquid that is at the point where it is ready to begin vaporizing. This occurs at a specific temperature and pressure, and the liquid is at equilibrium with its vapor phase, meaning it is 'saturated' and ready to turn into vapor without any additional heat.

How does a substance transition from a compressed liquid to a saturated liquid?

As heat is added to a compressed liquid at a constant pressure, its temperature increases until it reaches the boiling point. At this point, it becomes a saturated liquid, where it is on the verge of vaporizing into a gas. The transition happens at the saturation temperature for the given pressure.

What is the difference between saturated liquid and superheated steam?

Saturated liquid is a liquid at its boiling point, ready to vaporize at a given pressure, while superheated steam is steam that has been heated beyond the boiling point, at a constant pressure, without changing the phase. The temperature of superheated steam is higher than the saturation temperature.

What does the term 'latent heat' refer to in thermodynamics?

Latent heat refers to the amount of heat required to change the phase of a substance without changing its temperature. For example, the latent heat of vaporization is the energy needed to convert a liquid into a gas at its boiling point.

What is the critical point in a phase diagram?

The critical point on a phase diagram is the point at which the liquid and gas phases of a substance become indistinguishable. Beyond this point, the substance exists as a supercritical fluid, where distinct liquid and gas phases no longer exist.

How does pressure affect the boiling point of water?

The boiling point of water depends on the atmospheric pressure. At higher pressures, the boiling point increases, while at lower pressures, the boiling point decreases. This principle is used in technologies like vacuum frying.

What role does enthalpy play in thermodynamic analysis?

Enthalpy is a thermodynamic property that combines internal energy and the energy associated with pressure and volume (P*V). It is particularly useful in analyzing heat exchange processes, such as heating, cooling, or phase changes in a substance.