# Thermal decomposition of calcium carbonate - problem

• wuutoshi
In summary, calcium carbonate decomposes to calcium oxide and carbon dioxide. Some of the decomposed calcium carbonate is lost as CO2.
wuutoshi
Hello, here goes the problem:
The mass of calcium carbonate upon thermal decomposition decreased by 1/5. (a) How many molecules of CaCO3 per 100 molecules were decomposed to CaO and CO2. (b) The content of CaO in the final sample express in molar fraction.

My solution:
I set the starting sample to 100g which corresponds to 1 mole of CaCO3. The decrease of mass by 1/5 corresponds to 20g or 0.2 mole. So the solution seems to me to be 20 molecules per 100 molecules.
Ad (b) If 0.2 mole of CaCO3 were decomposed, 0.2 mole of CaO and 0.2 mole CO2 should be formed. Thus the molar fraction of CaO in final samples should be 0.2/(0.2+0.2+0.8) = 1/6.

Yet the provided solutions from two scources differs. Where, if so, did I make mistake?

wuutoshi said:
I set the starting sample to 100g which corresponds to 1 mole of CaCO3.

OK

The decrease of mass by 1/5 corresponds to 20g

OK

or 0.2 mole.

No. Mass decreased by 20 g, but it doesn't mean 20 g decomposed and disappeared.

Write reaction equation - what is lost during decomposition? What is left?

And please, don't ignore the template.

Borek said:
No. Mass decreased by 20 g, but it doesn't mean 20 g decomposed and disappeared.
CaCO3 → CaO + CO2

Doesn't 20 g of the decomposed reactant corresponds to decomposition of 0.2 mole of that reactant? I don't assume that mass dissappeares. It appears as 20 g of products (0.4 moles of them). So now we are left with 0.8 moles of CaCO3, isn't that true?

And please, don't ignore the template.

Ok.

Last edited:
I already asked you - what is lost, what is left? Add state symbols to all three substances and it should become obvious.

Should I assume that 20 g went away as CO2? So from 1 to 1 mole ratio, 0.45 moles of CaCO3 decomposed, which corresponds to 45 molecules per 100 molecules.
We are left with 0.45 moles of CaO and 0.55 moles of CaCO3 which is 45 % of CaO in the final sample.
Ok, the solutions agree.
Thank you, Borek, for making me think and approaching the problem from more real and "chemical point of view".

## 1. What is thermal decomposition of calcium carbonate?

Thermal decomposition of calcium carbonate is a chemical reaction in which calcium carbonate (CaCO3) breaks down into calcium oxide (CaO) and carbon dioxide (CO2) when heated to high temperatures.

## 2. What is the cause of the problem with thermal decomposition of calcium carbonate?

The problem with thermal decomposition of calcium carbonate is that it produces a significant amount of carbon dioxide gas, which is a major contributor to climate change and global warming.

## 3. How does thermal decomposition of calcium carbonate affect the environment?

Thermal decomposition of calcium carbonate contributes to the increase in atmospheric carbon dioxide levels, which can lead to the greenhouse effect and impact global temperatures and weather patterns. It also affects the pH of the surrounding soil and water, potentially harming ecosystems.

## 4. Can the problem of thermal decomposition of calcium carbonate be solved?

Yes, the problem of thermal decomposition of calcium carbonate can be mitigated by finding alternative methods for producing calcium oxide, such as using renewable energy sources instead of fossil fuels. Additionally, carbon capture and storage technologies can be used to capture and store the carbon dioxide produced during the decomposition process.

## 5. What are some potential applications of the thermal decomposition of calcium carbonate?

The thermal decomposition of calcium carbonate has various industrial applications, such as in the production of cement, lime, and other building materials. It is also used in agriculture to improve soil pH and as a supplement for plants to obtain calcium and reduce soil acidity.

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