Question

1. explain how the celsius scale was devised (what substances and temperatures is it based on? with which gas laws is it appropriate to use the celsius temperature scale?

Explanation:

1. Devising the Celsius Scale: Anders Celsius initially defined the Celsius scale using water. The lower fixed point (0 °C) was the temperature at which pure water freezes (or ice melts) at standard atmospheric pressure (1 atm), and the upper fixed point (100 °C) was the temperature at which pure water boils at 1 atm. Later, the definition was refined based on the triple point of water (the temperature and pressure at which water, ice, and water vapor coexist in equilibrium, which is 0.01 °C and 611.657 Pa) and the absolute zero - related definitions, but the common understanding of its initial basis is on water's phase change temperatures at 1 atm.
2. Gas Laws and Celsius Scale: The Celsius scale is appropriate for gas laws like Charles's Law (which relates the volume and temperature of a gas at constant pressure, \(V_1/T_1 = V_2/T_2\) where \(T\) is in Celsius for approximate calculations when the temperature change is considered relative to a reference, though the absolute temperature scale (Kelvin) is more fundamental for gas laws) and Gay - Lussac's Law (relates pressure and temperature of a gas at constant volume, \(P_1/T_1=P_2/T_2\) with similar caveats about relative temperature changes). However, it should be noted that for accurate gas law calculations, especially when dealing with absolute temperature - dependent relationships (like the ideal gas law \(PV = nRT\) where \(T\) is in Kelvin), the Celsius scale is used in cases where the temperature change (\(\Delta T\)) is considered, as \(\Delta T\) in Celsius is equal to \(\Delta T\) in Kelvin. For example, when studying the expansion of a gas in a balloon with a change in ambient temperature measured in Celsius, Charles's Law can be applied in a qualitative or approximate quantitative sense using Celsius temperatures for the temperature difference (since \(V\propto T\) and \(\Delta V\propto\Delta T\) where \(T\) can be in Celsius for the difference).

Answer:

• Devising the Celsius Scale: The Celsius scale was initially devised using water. At standard atmospheric pressure (1 atm), 0 °C was defined as the freezing (melting) point of pure water, and 100 °C was defined as the boiling point of pure water. Later, the definition was related to the triple point of water (0.01 °C at 611.657 Pa) and absolute zero.
• Gas Laws and Celsius Scale: It is appropriate for gas laws like Charles's Law (\(V\propto T\), where \(T\) can be in Celsius for temperature differences, as \(\Delta V\propto\Delta T\)) and Gay - Lussac's Law (\(P\propto T\), with similar usage for temperature differences in Celsius) in approximate or qualitative/quantitative (for temperature differences) applications. For accurate ideal gas law (\(PV = nRT\)) calculations, Kelvin is the fundamental scale, but Celsius can be used for temperature change - based gas law applications.