Specification Point 5.13C:
Recall the atom economy of a reaction forming a desired product.
- Along with the percentage yield, atom economy is used to analyse the efficiency of reactions.
- Atom economy studies the amount of reactants that get turned into useful products.
- It illustrates what percentage of the mass of reactants become useful products.
- It is used extensively in the analysis of systems and procedures in industries, in an effort to obtain sustainable development.
- It is also a very important analysis for economical reasons as companies prefer to use processes with higher atom economies.
- The higher the atom economy of a process then the more sustainable that process is.
Calculating Atom Economy
Specification Point 5.14C:
Calculate the atom economy of a reaction forming a desired product.
Atom economy = (total Mr of desired product ÷ total Mr of all products) x 100
Hydrogen gas is obtained from methane in a process called steam-methane reforming. Calculate the atom economy of this reaction.
Equation Of Reaction:
CH4 (g) + H2O (g) → CO (g) + 3H2 (g)
Step 1 Calculate the total Mr of all the products:
Total Mr = 28 (CO:12 + 16) + (3H2: 6 x 1) = 34
Step 2 Calculate the Mr of the desired products:
Mr of 3H2 (6 x 1) = 6
Step 3 Calculate the atom economy:
Atom economy = (6 ÷ 34) x 100 = 17.6%
Therefore in this process 82% by mass of reactants is wasted.
Edexcel GCSE Chemistry Notes
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