Structure 1.1.3—The temperature, T , in Kelvin (K) is a measure of average kinetic energy *E*k of particles

Interpret observable changes in physical properties and temperature during changes of state.

Convert between values in the Celsius and Kelvin scales.

**What You’ll Learn:**

- The Kelvin (K) is the SI unit of temperature and has the same incremental value as the Celsius degree (°C).

**Keywords**

melting, freezing, vaporization, evaporation, boiling, condensation, sublimation and deposition

**Syllabus Links**

Reactivity 2.2—What is the graphical distribution of

kinetic energy values of particles in a sample at a

fixed temperature?

Reactivity 2.2—What must happen to particles for a

chemical reaction to occur?

The Kelvin Scale

The Kelvin (K) is the standard unit of temperature in the International System of Units (SI). It is named after William Thomson, also known as Lord Kelvin, a renowned physicist and engineer who made significant contributions to the field of thermodynamics. Kelvin is widely used in scientific applications and is preferred over other temperature units due to its unique properties.

The Kelvin scale is based on the concept of absolute zero, which is the temperature at which all molecular motion ceases. Absolute zero is calculated to be -273.15°C, which is also known as 0 Kelvin. This means that Kelvin starts at absolute zero, and each Kelvin unit is equal to one Celsius degree. Therefore, a temperature difference of 1 Kelvin is equivalent to a temperature difference of 1 Celsius degree.

Unlike the Celsius scale, which is based on the freezing and boiling points of water, the Kelvin scale is based on the theoretical concept of absolute zero. This makes the Kelvin scale an ideal temperature unit for scientific applications. It is used extensively in fields such as physics, chemistry, and engineering, where precise temperature measurements are essential.

T(K) = T(°C) + 273.15

One of the significant advantages of the Kelvin scale is that it is an absolute temperature scale. This means that Kelvin values can be directly proportional to the amount of thermal energy in a system. It is also the reason why Kelvin is the preferred unit of temperature in scientific experiments involving thermodynamic calculations. It allows scientists to study the relationship between temperature, pressure, and volume, which is essential in understanding the behavior of gases and other materials.

Questions

- What is the Kelvin scale, and why is it preferred over other temperature units?
- What is absolute zero, and how is it related to the Kelvin scale?
- How does the Kelvin scale differ from the Celsius scale, and why is it ideal for scientific applications?
- How is the relationship between temperature, pressure, and volume important in understanding the behavior of gases and other materials?
- How is the Kelvin scale used in scientific experiments involving thermodynamic calculations?

Graph Task

What is the relationship between temperature and pressure in a gas, use 10 data points to plot a graph and extrapolate the data to estimate the pressure at absolute zero?

Plot a graph of the relationship between temperature and pressure in a gas:

Temperature (K) | Pressure (kPa) |

100 | 377 |

150 | 430 |

200 | 480 |

250 | 535 |

300 | 584 |

350 | 636.5 |

400 | 690.5 |

450 | 740 |

500 | 794.5 |

550 | 845 |

Note: The data points are just an example, and the actual data used to plot the graph should be based on the specific gas being studied and the conditions under which the measurements were taken.

To plot the data in Excel and extrapolate it to estimate the pressure at absolute zero, follow these steps:

- Enter the temperature and pressure data into two columns in Excel.
- Select the columns containing the data by clicking and dragging over the cells.
- Click on the “Insert” tab in the Excel ribbon, then select the “Scatter” chart type.
- Choose the scatter chart type that best suits your data (e.g., a line chart with markers or a scatter chart with smooth lines and markers).
- Right-click on the data series in the chart and select “Add Trendline”.
- In the “Format Trendline” pane that appears on the right-hand side of the screen, select the “Linear” trendline option.
- Check the box labeled “Display equation on chart” to display the equation for the trendline on the chart.
- Use the equation to estimate the pressure at absolute zero by substituting 0 Kelvin for temperature in the equation and solving for pressure.

To extrapolate the data back to the y-axis (pressure) intercept, follow these additional steps:

- Right-click on the y-axis in the chart and select “Format Axis”.
- In the “Format Axis” pane that appears on the right-hand side of the screen, check the box labeled “Axis Options” and set the minimum value to 0.
- Use the equation for the trendline to estimate the y-axis intercept (i.e., the pressure at 0 Kelvin) by setting the temperature to 0 Kelvin in the equation and solving for pressure. This value represents an estimate of the pressure at absolute zero based on the trendline equation and should be interpreted with caution as extrapolation beyond the range of the data is uncertain and may be affected by factors not accounted for by the model.