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Ch.9 - Thermochemistry: Chemical Energy
Chapter 9, Problem 100

What phase of matter is associated with the standard states of the following elements and compounds? (a) Cl2 (b) Hg (c) CO2 (d) Ga

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Identify the standard state of each element or compound at room temperature (25°C or 298 K) and 1 atmosphere pressure.
For Cl2 (chlorine), recognize that it is a diatomic molecule and typically exists as a gas under standard conditions.
For Hg (mercury), note that it is unique among metals as it is in a liquid state at room temperature.
For CO2 (carbon dioxide), consider its common use and occurrence, primarily existing as a gas at standard conditions.
For Ga (gallium), remember that it has a melting point of about 29.76°C, which is slightly above room temperature, making it a solid at 25°C.

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Key Concepts

Here are the essential concepts you must grasp in order to answer the question correctly.

Phases of Matter

The phases of matter refer to the distinct forms that different phases of matter take on. The most common phases are solid, liquid, and gas, which are determined by the arrangement and energy of particles. Understanding these phases is crucial for identifying the standard states of elements and compounds at a given temperature and pressure.
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Standard State

The standard state of a substance is defined as its most stable physical form at a specified temperature (usually 25°C) and pressure (1 atm). This concept is essential for determining the phase of matter for elements and compounds, as it provides a reference point for their physical properties under standard conditions.
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Element and Compound Properties

Elements and compounds exhibit specific properties that dictate their phase at standard conditions. For example, some elements like chlorine (Cl2) are gases, while others like mercury (Hg) are liquids at room temperature. Understanding these properties helps in predicting the phase of various substances based on their molecular structure and intermolecular forces.
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