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Chemical Calculations

 How carbon dioxide is removed in spacecraft? How carbon dioxide is removed in spacecraft? The carbon dioxide in the Earth's atmosphere is used up by the process of photosynthesis. The plants take in carbon dioxide and release oxygen. However, in a spacecraft, carbon dioxide is removed through chemical processes. The air scrubber used in spacecraft contain lithium hydroxide (LiOH). When air containing carbon dioxide (CO2) gets passed through the scrubber, it combines with the lithium hydroxide (LiOH) to form lithium carbonate (Li2CO3) and water (H2O).
CO2 (g) + 2LiOH (s)  →  Li2CO3 (s) + 3H2O (l)
Based on the average human production of CO2 and number of days of mission, by using the above balanced stoichiometric equation, the amount of LiOH to be taken with the space craft is calculated.

Learning Objectives

After completing the topic, the student will be able to:

  • Appreciate the role of stoichiometry in chemistry.
  • Recall the conversion factors.
  • Use the conversion factors to change one physical quantity to other.
  • Restate the standard definition of fundamental units.
  • Write the relationships between a chemical formula as a whole and the individual atoms in that formula using conversion factors.
  • Identify the limiting reagent in a chemical reaction by following a conversion sequence.
  • Determine the theoretical yield in chemical reaction.
  • Calculate the percentage yield in chemical reaction.
  • Calculate the mass percentage of an element in the given compound by identifying the molecular formula.
  • Define and determine empirical formula and molecular formula.
 Law of conservation of mass Law of conservation of mass Total mass of reactants before reaction is equal to total mass of products after the reaction.
Stoichiometry

In the late 1700's, a French noble man named Antoine Lavoisier observed that the total mass of all substances present after a chemical reaction is same as total mass before the reaction. This observation, known as the law of conservation of mass, is one of the fundamental laws of chemical change. In 1789, Lavoisier published a text book on chemistry in which he stated “We may lay it down as an incontestable axiom that, in all the operations of art and nature, nothing is created; an equal quantity of matter exists both before and after the experiment”.

With the outcome of atomic theory chemists came to understand the basis for this law: Atoms are neither created nor destroyed during any chemical reaction. Thus number of atoms remains constant before and after the completion of reaction. The changes that occur during any reaction merely involve rearrangement of atoms. Lavoisier medal is given to honor people throughout the history of DuPont whose extraordinary technical achievements have resulted in significant business impact and enduring scientific value. With this knowledge, we now move forward to examine the quantitative nature of chemical formulas and chemical reactions. This area of study is called stoichiometry.

Pictorial demonstration of Lavoisier's experiment Pictorial demonstration of Lavoisier's experiment Mass is conserved during the reaction.
Lavoisier's experiment

Lavoisier hypothesized that mass is always conserved during a chemical reaction, where conserved in this context means that the amount of the mass does not change. The number of grams of mass present after the reaction is the same as the number of grams present before the reaction.

Lavoisier measured the mass of a sealed glass vessel containing tin and the mass of the same vessel containing a white powder left after the tin underwent a chemical reaction. He found the mass to be the same before and after the reaction.

Calcination experiments on tin in sealed glass vessel have shown that weight is conserved during the reaction. But there was gain in weight of vessel afterwards due to rusting process which was not understood at his time.

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