Textbook Question
CO₂ exists in what phase when the pressure is 35 atm, and the temperature is 35°C (Fig. 18–6)?
20. Heat and Temperature
Phase Diagrams, Triple Points and Critical Points
1:59 minutesProblem 26a
Textbook Question
Water is in which phase when the pressure is 0.01 atm and the temperature is 90°C?
Verified step by step guidance1
Understand the problem: The question asks about the phase of water at a specific pressure (0.01 atm) and temperature (90°C). To determine the phase, we need to compare these conditions to the phase diagram of water, which shows the relationship between pressure, temperature, and phase (solid, liquid, or gas).
Recall the concept of a phase diagram: A phase diagram is a graphical representation of the states of matter (solid, liquid, gas) of a substance as a function of pressure and temperature. For water, the phase diagram includes the triple point (where all three phases coexist) and the critical point (beyond which liquid and gas are indistinguishable).
Locate the given conditions on the phase diagram: At a pressure of 0.01 atm, check the temperature range for the phase boundaries. The triple point of water occurs at approximately 0.006 atm and 0.01°C. At 0.01 atm, the boiling point of water (liquid-gas boundary) is significantly lower than 100°C, and water is likely in the gas phase at 90°C.
Analyze the phase boundaries: Since the given temperature (90°C) is well above the boiling point of water at 0.01 atm, the water will have transitioned to the gas phase. This is because the liquid phase cannot exist at such low pressures and high temperatures.
Conclude the phase: Based on the analysis of the phase diagram, water is in the gas phase (steam) at a pressure of 0.01 atm and a temperature of 90°C.
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Key Concepts
Here are the essential concepts you must grasp in order to answer the question correctly.
Phase of Matter
The phase of matter refers to the distinct forms that different phases of matter take on. The three primary phases are solid, liquid, and gas, each characterized by different properties such as shape and volume. Understanding the phase of a substance is crucial for predicting its behavior under varying conditions of temperature and pressure.
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Phase Diagram
A phase diagram is a graphical representation that shows the phases of a substance at different temperatures and pressures. It typically includes lines that separate different phases, indicating the conditions under which a substance will exist as a solid, liquid, or gas. Analyzing a phase diagram helps in determining the state of a substance at specific temperature and pressure conditions.
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Boiling Point and Vapor Pressure
The boiling point of a liquid is the temperature at which its vapor pressure equals the external pressure surrounding it. At lower pressures, such as 0.01 atm, the boiling point of water decreases significantly. This concept is essential for understanding how water can exist in different phases under varying pressure conditions, particularly in relation to its boiling point.
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