Have you ever heard of gold cyanidation? An aqueous cyanide solution is used to treat crushed gold ore in the presence of air, forming a soluble gold compound, which can then be further reduced to recover pure gold.
The skeleton equation for this reaction is given as:
\( \text{Au} \text{ + NaCN + } \text{O}_{2} + \text{H}_{2}\text{O} \longrightarrow \text{Na(Au(CN)}_{2}) + \text{NaOH}\).
But what does this mean? Let's explore what skeleton equations are!
- First, we will talk about chemical reactions and balanced equations.
- Then, we will look at the definition of a skeleton equation.
- After, we will learn how to write a skeleton equation and explore some chemical reactions involving ethanol
- Lastly, we will look at some examples of skeleton equations.
Skeleton Equation vs. Balanced Equation
Before we get into what a skeleton equation is, let's review chemical reactions. In chemical reactions, the bonds between atoms in the reactant side are broken, and new bonds are formed, creating new substances.
$$ \text{Reactant + Reactant } \longrightarrow \text{ Products} $$
In chemistry, chemical reactions involve the transformation of one or more substances into new ones.
When a chemical reaction happens, any of the following might occur:
- Changes in temperature.
- Changes in color.
- Formation of gases, bubbles, or odor.
- Formation of a solid (precipitate).
- Energy release.
Chemists use chemical equations to represent these changes happening in a chemical reaction.
The chemical equation is a representation of a chemical reaction.
For example, the chemical equation between the reactants carbon monoxide gas (CO) and oxygen gas (O2) to yield carbon dioxide (CO2) is shown below:
$$ \text{2 CO + O}_{2} \longrightarrow 2 \text{ CO}_{2} $$
Chemical equations follow the law of conservation of mass. According to this law, the mass of the products is always the same as the mass of the reactants. Therefore, chemicals equations must be balanced to make sure the law of conservation of mass in being followed.
Balanced chemical equations are those in which the number of atoms of each element on the left is equal to the number of atoms on the right.
Let's look at an example!
Balance the following chemical equation: \(\text{H}_{2} \text{ + O}_{2} \longrightarrow \text{H}_{2}\text{O}\).
To balance a chemical equation, we need to figure out the exact coefficients that will give us equal numbers atoms on both sides of the equation.
- In a chemical equation, the coefficient is the number written in front of the reactant or product, and it tells us the lowest whole-number ratio of the amounts of reactants and products.
Now, notice that on the left side (the reactant side) of the equation, we have 2 atoms of oxygen and 2 atoms of hydrogen. On the right side (product side), we have 2 atoms of hydrogen and 1 atom of oxygen.
Figure 1. Balancing a chemical equation part one, Isadora Santos - Vaia Originals.
So, we can start by finding the right coefficient to equal the number of oxygen atoms on both sides. If a coefficient of 2 is added in front of H2O, it will cause the number of atoms on right side to change to 2 atoms of oxygen and 4 hydrogen atoms.
Figure 2. Balancing a chemical equation part two, Isadora Santos - Vaia Originals.
Now, we need to balance the number of atoms of hydrogen so that we can have 4 atoms of hydrogen on both sides. To achieve this, we can add a coefficient of 2 to the H₂ on the left side.
Figure 3. Balancing a chemical equation part three, Isadora Santos - Vaia Originals.
Now, we have a balanced equation containing 4 hydrogen atoms and 2 atoms of oxygen on each side! This tells us that 2 moles of H₂ reacts with 1 mol of O2 to form 2 moles of water (H2O).
$$ \color {#1478c8} 2 \color {black}\text{ H}_{2} \text{ + O}_{2} \longrightarrow \color {#1478c8} 2\color {black} \text{ H}_{2}\text{O} $$
Looking for more information on balanced chemical reactions? Check out "Balancing Equations"!
Skeleton Equation Definition
Now that we know what balanced equations are, let's look at the definition of a skeleton equation.
A skeleton equation is simply an unbalanced chemical equation. In other words, the relative amounts of products and reactants are not shown in skeleton equations.
As an example, let's look at the chemical reaction between iron (Fe) and chlorine gas (Cl2) to yield iron (III) chloride (FeCl3). The skeletal equation for this reaction would be:
$$ \text{Fe }(s)\text{ + Cl}_{2}\text{ } (g) \longrightarrow \text{FeCl}_{3}\text{ }(s) $$
Now, if we were to balance this equation, we would get:
$$ \text{2 Fe }(s)\text{ + 3 Cl}_{2}\text{ } (g) \longrightarrow \text{2 FeCl}_{3}\text{ }(s) $$
How to Write a Skeleton Equation
To write a skeleton equation, all you need to do is know the reactants you are dealing with and the product it forms!
For example, if you were told that there was a chemical reaction happening between aluminum and oxygen in which aluminum oxide was formed, you can use this word equation to write the reaction's skeleton equation.
Skeleton equation: \(\text{Al} (s) \text{ + O}_{2}(g) \longrightarrow \text{Al}_{2}\text{O}_{3}(s)\)
Balanced equation: \( \text{4 Al} (s) \text{ + 3 O}_{2}(g) \longrightarrow \text{2 Al}_{2}\text{O}_{3}(s) \)
Let's solve a problem!
Write the skeleton equation for a chemical reaction happening between hydrochloric acid and calcium hydroxide. This reaction yields calcium chloride and water.
First things first. We need to write down each of these compounds using their chemical symbols. In this case, hydrochloric acid is written as HCl, calcium hydroxide is written as Ca(OH)2, calcium chloride as CaCl2 and water as H2O.
Now, we can write down the skeleton equation for this chemical reaction!
$$ \text{HCl + Ca(OH)}_{2} \longrightarrow \text{CaCl}_{2} \text{ + }\text{H}_{2}\text{O} $$
Skeleton Equation of Methanol
Now that we've discussed skeleton equations and how to write them, let's look at some skeleton equations involving methanol (CH3OH).
Methanol is a liquid at STP, and it is miscible in water. It is considered a volatile liquid alcohol, and it widely used as antifreeze and fuel. The Lewis structure of methanol is shown below:
Let's first look at the chemical reaction between methanol and water. In this reaction, carbon dioxide and hydrogen gas are produced! The skeleton equation for this reaction is as follows:
\text{CH}_{3}\text{OH + H}_{2}\text{O} \rightleftharpoons \text{CO}_{2}\text{ + H}_{2}
When methanol is allowed to react with oxygen, it forms formaldehyde (HCHO) and hydrogen peroxide (H2O2) as products. Formaldehyde is a colorless gas produced by the oxidation of methanol. It is considered poisonous.
The skeleton equation in this case is
\( \text{CH}_{3}\text{OH + O}_{2} \longrightarrow \text{HCHO}\text{ + H}_{2}\text{O}_{2} \).
Notice that, in this case, the balanced chemical equation for the reaction between methanol and oxygen would be the same as the skeleton equation!
Now, what happens when methanol (CH3OH) reacts with a metal like sodium? The reaction between methanol and sodium (Na) yields sodium methoxide and hydrogen!
Skeleton equation:
\( \text{CH}_{3}\text{OH + Na}\longrightarrow \text{NaOCH}_{3}\text{ +}\text{ H}_{2}\)
Balanced equation:
\( \text{2 CH}_{3}\text{OH + 2 Na}\longrightarrow \text{2 NaOCH}_{3}\text{ +}\text{ 3 H}_{2}\)
Skeleton Equation Examples
To finish off, let's look at some examples involving the skeleton equation of some important chemical reactions.
For example, in biology, some bacteria (such as H. pylori) are able to degrade urea (H2NCONH2) into ammonia (NH3) and carbon dioxide (CO2)
Skeleton equation:
\( \text{H}_{2}\text{NCONH}_{2} + \text{H}_{2}\text{O} \longrightarrow \text{NH}_{3} +\text{ CO}_{2}\)
Balanced equation:
\( \text{H}_{2}\text{NCONH}_{2} + \text{H}_{2}\text{O} \longrightarrow \text{2 NH}_{3} +\text{ CO}_{2}\)
Another interesting chemical reaction is the formation of ozone (O3), which occurs when a monatomic oxygen molecule (O) combines with a diatomic oxygen molecule (O2). Ozone is a gas that is commonly produced by the action of UV radiation on oxygen in the stratosphere, causing its photodissociation. The earth's ozone layers acts a screen, blocking most UV radiation coming form the sun.
Skeleton equation:
\(\text{O + O}_{2}\longrightarrow \text{O}_{3}\)
Balanced equation:
\( \text{O + 2 O}_{2}\longrightarrow \text{2 O}_{3}\)
I hope you've now got a better idea of what a skeleton equation is!
Skeleton Equation - Key takeaways
- In chemistry, chemical reactions involve the transformation of one or more substances into new ones.
- Balanced chemical equations are those in which the number of atoms of each element on the left is equal to the number of atoms on the right.
- A skeleton equation is simply an unbalanced chemical equation. The relative amounts of products and reactants are not shown in skeleton equations.
References
- Zumdahl, S. S., Zumdahl, S. A., & Decoste, D. J. (2019). Chemistry. Cengage Learning Asia Pte Ltd.
- Theodore Lawrence Brown, Eugene, H., Bursten, B. E., Murphy, C. J., Woodward, P. M., Stoltzfus, M. W., & Lufaso, M. W. (2018). Chemistry : the central science (14th ed.). Pearson.
- Swanson, J. (2021). Everything you need to ace chemistry in one big fat notebook. Workman.
- Moat, A. G., Foster, J. W., & Spector, M. P. (2003). Microbial Physiology. John Wiley & Sons.
Explanations 
Textbooks 
Exams 
Magazine 
