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Chapter 5: Problem 17

According to the law of conservation of mass, mass cannot be gained or destroyed in a chemical reaction. Why can't you simply add the masses of two reactants to determine the total mass of product?

Short Answer

Expert verified
In a chemical reaction, atoms within reactant molecules rearrange themselves to form product molecules, so merely adding the masses of reactants will not give the exact mass of products. We must balance the chemical equation, use mole ratios, and consider the rearrangement of atoms to determine the total mass of products accurately. The law of conservation of mass holds true at an atomic level, meaning the number and type of atoms remain constant in a closed system throughout the reaction.

Step by step solution

01

: In a chemical reaction, atoms within reactant molecules rearrange themselves to form product molecules. The total mass of atoms remains conserved, but the individual masses of different types of molecules may change. Therefore, merely adding the masses of reactants will not give you the exact mass of products. #Step 2: Balancing the chemical equation#

: Before determining the mass of products, we need to balance the chemical equation to ensure the number of atoms in reactants and products is the same for each element. By following the law of conservation of mass, we can ensure that the correct amount of reactants is used, and the correct mass of products is formed. #Step 3: Using mole ratios to find the total mass of product#
02

: Once the chemical equation is balanced, we can use the mole ratio of reactants and products to determine the mass of each product formed. We establish these relationships by converting the masses of reactants into moles, using the molecular weights of each substance. For example, if the balanced equation is: \[A + 2B \to C + 3D\] Suppose the mass of 'A' and 'B' reactants are given. To determine the mass of products 'C' and 'D', you would: 1. Convert the mass of reactant 'A' to moles using its molecular weight 2. Convert the mass of reactant 'B' to moles using its molecular weight 3. Compare the mole ratios in the balanced equation and see which reactant is in excess or limiting 4. Determine the moles of products 'C' and 'D' according to the balanced equation 5. Convert the moles of product 'C' back into mass using its molecular weight 6. Convert the moles of product 'D' back into mass using its molecular weight 7. Sum the masses of 'C' and 'D' to find the total mass of products #Step 4: Recognizing that mass is conserved at an atomic level#

: In conclusion, the reason why we can't simply add the masses of reactants to determine the total mass of products is that a chemical reaction involves the rearrangement of atoms, not just the combination of masses. We must consider the balanced chemical equation and the corresponding mole ratios to accurately determine the total mass of product. The law of conservation of mass still holds true but at an atomic level, meaning the number and type of atoms remain constant in a closed system throughout the reaction.

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Most popular questions from this chapter

A sample of urea contains \(1.121 \mathrm{g} \mathrm{N}, 0.161 \mathrm{g} \mathrm{H}, 0.480 \mathrm{g} \mathrm{C}\) and \(0.640 \mathrm{g}\) O. What is the empirical formula of urea?

A potential fuel for rockets is a combination of \(\mathrm{B}_{5} \mathrm{H}_{9}\) and \(\mathrm{O}_{2}.\) The two react according to the following balanced equation: $$2 \mathrm{B}_{5} \mathrm{H}_{9}(l)+12 \mathrm{O}_{2}(g) \longrightarrow 5 \mathrm{B}_{2} \mathrm{O}_{3}(s)+9 \mathrm{H}_{2} \mathrm{O}(g)$$ If one tank in a rocket holds \(126 \mathrm{g} \mathrm{B}_{5} \mathrm{H}_{9}\) and another tank holds \(192 \mathrm{g} \mathrm{O}_{2},\) what mass of water can be produced when the entire contents of each tank react together?

The space shuttle environmental control system handles excess \(\mathrm{CO}_{2}\) (which the astronauts breathe out; it is \(4.0 \%\) by mass of exhaled air) by reacting it with lithium hydroxide, LiOH, pellets to form lithium carbonate, \(\mathrm{Li}_{2} \mathrm{CO}_{3}\), and water. If there are seven astronauts on board the shuttle, and each exhales 20. L of air per minute, how long could clean air be generated if there were 25,000 g of LiOH pellets available for each shuttle mission? Assume the density of air is 0.0010 g/mL.

DDT, an insecticide harmful to fish, birds, and humans, is produced by the following reaction: $$2 \mathrm{C}_{6} \mathrm{H}_{5} \mathrm{Cl}+\mathrm{C}_{2} \mathrm{HOCl}_{3} \longrightarrow \mathrm{C}_{14} \mathrm{H}_{9} \mathrm{Cl}_{5}+\mathrm{H}_{2} \mathrm{O}$$ In a government lab, 1142 g of chlorobenzene is reacted with 485 g of chloral. a. What mass of DDT is formed, assuming \(100 \%\) yield? b. Which reactant is limiting? Which is in excess? c. What mass of the excess reactant is left over? d. If the actual yield of DDT is \(200.0 \mathrm{g},\) what is the percent yield?

Ammonia reacts with \(\mathrm{O}_{2}\) to form either \(\mathrm{NO}(g)\) or \(\mathrm{NO}_{2}(g)\) according to these unbalanced equations: $$\begin{array}{l}\mathrm{NH}_{3}(g)+\mathrm{O}_{2}(g) \longrightarrow \mathrm{NO}(g)+\mathrm{H}_{2} \mathrm{O}(g) \\\\\mathrm{NH}_{3}(g)+\mathrm{O}_{2}(g) \longrightarrow \mathrm{NO}_{2}(g)+\mathrm{H}_{2} \mathrm{O}(g)\end{array}$$ In a certain experiment 2.00 moles of \(\mathrm{NH}_{3}(g)\) and 10.00 moles of \(\mathbf{O}_{2}(g)\) are contained in a closed flask. After the reaction is complete, 6.75 moles of \(\mathbf{O}_{2}(g)\) remains. Calculate the number of moles of \(\mathrm{NO}(g)\) in the product mixture: (Hint: You cannot do this problem by adding the balanced equations because you cannot assume that the two reactions will occur with equal probability.)
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