# When 60g of calcium carbonate is heated, 16.8g of Calcium oxide are formed. What is the percentage yield? (multiple choice)

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When calcium carbonate is heated it decomposes according to the equation:

#"CaCO"_3 -> "CaO" + "CO"_2#

A. 16.8%

B. 25%

C. 50%

D. 60%

The answer is C. 50%, why?

When calcium carbonate is heated it decomposes according to the equation:

A. 16.8%

B. 25%

C. 50%

D. 60%

The answer is C. 50%, why?

##### 1 Answer

#### Answer:

#### Explanation:

Start by taking a second to make sure that you understand what the problem wants you to determine.

A reaction's **percent yield** will essentially tell you one thing - how *efficient* said reaction is.

In this context, the **more efficient** a reaction, the closer it will be to **theoretical production**, which is what we calculate assuming that absolutely every molecule of the reactants will *actually react* to form the desired product.

The **theoretical yield** of a reaction will thus correspond to a **yield**. The **actual yield**, which is what you get in practice, will correspond to the reaction's **percent yield**.

So, the problem wants you to figure out how efficient this reaction is at producing calcium oxide,

#"CaCO"_text(3(s]) stackrel(color(red)(Delta)color(white)(aa))(->) "CaO"_text((s]) + "CO"_text(2(g])# #uarr#

So, what would you **theoretical yield** be?

Well, in theory, **every mole** of calcium carbonate that undergoes **decomposition** should produce **one mole** of calcium oxide.

Take a look at the 8*molar masses** of the two compounds

#"For CaCO"_3: " "M_M = "100.09 g mol"^(-1)#

#"For CaO: " M_M = "56.08 g mol"^(-1)#

So, if one mole of calcium carbonate should produce one mole of calcium oxide, it follows that

This means that

#60 color(red)(cancel(color(black)("g CaCO"_3))) * "56.08 g CaO"/(100.09color(red)(cancel(color(black)("g CaCO"_3)))) = "33.65 g CaO"#

You know that your reaction **actually** produced

#16.8color(red)(cancel(color(black)("g CaO"))) * overbrace("100% yield"/(33.65color(red)(cancel(color(black)("g CaO")))))^(color(purple)("theoretical yield")) = 49.9% ~~ color(green)("50%")#

This is exactly what the formula for percent yield gets you

#color(blue)("% yield" = "what you actually get"/"what you should theoretically get" xx 100)#