Scientific Understanding

**How do temperature conversions work?**

If you want to know more about temperature go back to the temperature section in the states of matter lesson. What you need to learn from this section is how to convert between the temperature scales (units to measure temperature). Because temperature devices were so difficult to make until about 1900, different people came up with different temperature scales. As a result, we are left with some temperature scales that are quite useless. The Fahrenheit temperature scale is one of those relics that is left over. The daily or morning news in America gives predicted temperatures in the Fahrenheit scale. However, the Celsius scale is a far better temperature measurement system for us to use on earth. If you want to know how to convert between Fahrenheit and Celsius scale go to this link. Most students don’t need to know how to convert between Fahrenheit and Celsius so I will not teach it on this page. The Celsius scale was set up to revolve around the temperature that water will freeze at on earth if the Celsius measurement is zero. This is significant to all life on Earth, since all life on earth needs water to survive. However, after you leave our tiny little planet of Earth the Celsius scale loses it meaning. That is why the Kelvin scale was created. The Kelvin scale works everywhere in the universe, which is the best kind of scale to use for any mathematical calculations you have to do (like chemistry formulas). The reason why it works anywhere is because the Kelvin scale is a true measurement of how molecules or particles move. At zero degrees Kelvin all molecule or particle movement stops. This is why we will eventually use the Kelvin scale for nearly all of our chemistry calculations. Now lets try looking at the formula for converting between the Celsius temperature scale and the Kelvin temperature scale.

Celsius to Kelvin:

K = C + 273

The letter K represents the temperature in Kelvin and the letter C represents the temperature in Celsius.

**Examples**: Convert the following temperature units.

What is the Kelvin measurement of 150 C?

Answer: 423 K

What is the Celsius measurement of 240K?

Answer: -33 C

**VIDEO Temperature Conversions Demonstrated Example 1**: If the temperature is 25 C what is the Kelvin temperature?

**Step 1:**

What information are we given?

Answer: 25 C

**Step 2:**

What units does the question ask for?

Answer: Kelvin

**Step 3:**

How do we set up the problem?

Answer: Start with the equation

K = | C + 273 |

**Step 4:**

What can we fill in for the equation?

Answer: The information we are given (red).

K = | 25 + 273 |

**Step 5:**

How do I do the calculations?

25 + 273 = 298

**Step 6:**

What is the complete answer?

COMPLETE ANSWER: 298 K

**VIDEO Temperature Conversions Demonstrated Example 2**: If the temperature is 800 K what is the Celsius temperature?

**Step 1:**

What information are we given?

Answer: 800 K

**Step 2:**

What units does the question ask for?

Answer: Celsius

**Step 3:**

How do we set up the problem?

Answer: Start with the equation

K = | C + 273 |

**Step 4:**

What can we fill in for the equation?

Answer: The information we are given (red).

800 = | C + 273 |

**Step 5:**

How do we rearrange the equation?

Answer: Subtract 273 from both sides

800 -273 = | C + 273 -273 |

**Step 6:**

Simplify by canceling the positive and negative 273 on the right side.

800 -273= | C |

**Step 7:**

How do I do the calculations?

Answer: 800 – 273 = 527

**Step 8:**

What is the complete answer?

COMPLETE ANSWER: 527 C

**PRACTICE PROBLEMS**: Convert between Kelvin and Celsius in the questions below.

What is the Kelvin temperature if it is 312 C?

Answer: 585 K

What is the Celsius temperature if it is 218 K?

Answer: -55 C

What is the Kelvin temperature if it is 40 C?

Answer: 313 K

What is the Celsius temperature if it is 382 K?

Answer: 109 C