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Chapter 3: Problem 79

Define limiting reagent and excess reagent. What is the significance of the limiting reagent in predicting the amount of the product obtained in a reaction? Can there be a limiting reagent if only one reactant is present?

Short Answer

Expert verified
The limiting reagent determines the maximum product formed; it can't exist with only one reactant.

Step by step solution

01

Understanding Reagents

In a chemical reaction, reactants are substances that start the reaction, while products are the substances formed as a result of the reaction. In most reactions, one or more reactants are used up completely, while others might be in excess.
02

Defining Limiting Reagent

The limiting reagent, or limiting reactant, is the substance that is entirely consumed first during a chemical reaction. It limits the extent of the reaction and determines the maximum amount of product that can be formed as it runs out before the other reactants.
03

Defining Excess Reagent

The excess reagent or excess reactant is the substance that remains after the limiting reagent is completely used up. There is more of this reagent than necessary to completely react with the amount of the limiting reagent available.
04

Significance of Limiting Reagent

The significance of the limiting reagent is that it dictates the maximum amount of product that can be formed in a chemical reaction. By identifying the limiting reagent, chemists can calculate the theoretical yield of a reaction, ensuring efficient use of resources.
05

Case of Single Reactant

If only one reactant is present, there cannot be a limiting reagent in the context of the reaction because a limiting reagent is related to the presence of multiple reactants, where one limits the reaction. With a single reactant, the reaction is dependent solely on the amount of that substance available.

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Key Concepts

These are the key concepts you need to understand to accurately answer the question.

Excess Reagent
In a chemical reaction, the excess reagent is the reactant that is not completely used up when the reaction reaches completion. Think of it like having extra toppings left after making a pizza. It simply means there was more of this ingredient than needed for the recipe.
Understanding the presence of an excess reagent helps chemists to know that not all materials were converted into products. Knowing this can also be useful for recycling or recovering unused materials, which can be economical in large-scale reactions.
  • Interestingly, the amount of excess reagent can be calculated once the limiting reagent is known.
  • The excess reagent can sometimes be reused in subsequent reactions.
This concept ensures that chemical processes are efficient, allowing chemists to manage resources wisely.
Chemical Reaction
A chemical reaction involves transforming reactants into products. In this transformative process, bonds between atoms are broken and new ones are formed.
Chemical reactions are the backbone of chemistry and occur all around us, from the rusting of iron to the photosynthesis in plants.
There are different types of chemical reactions, such as combustion, synthesis, decomposition, and double replacement reactions. Each type has its own unique characteristics:
  • Combustion involves burning a substance in oxygen to release energy.
  • Synthesis means combining simpler substances to form a more complex molecule.
  • Decomposition involves breaking a compound into simpler substances.
  • Double replacement involves the exchange of ions between two compounds.
Understanding these reactions helps predict how substances interact and transform.
Theoretical Yield
The theoretical yield is the maximum amount of product expected from a chemical reaction, assuming no losses or side reactions. It represents an ideal scenario where everything reacts perfectly to completion.
Calculating the theoretical yield requires a balanced chemical equation and knowing which reactant is the limiting reagent.
  • First, determine the moles of limiting reagent available.
  • Use stoichiometry to calculate the potential moles of product.
  • Convert moles of product to grams if needed, using molar masses.
In real-world settings, the actual yield is often less than the theoretical yield due to factors like incomplete reactions or side products. Therefore, understanding theoretical yield helps chemists aim for more efficient processes while considering potential losses.

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Most popular questions from this chapter

A compound X contains 63.3 percent manganese (Mn) and 36.7 percent O by mass. When \(X\) is heated, oxygen gas is evolved and a new compound Y containing 72.0 percent \(\mathrm{Mn}\) and 28.0 percent \(\mathrm{O}\) is formed. (a) Determine the empirical formulas of \(X\) and Y. (b) Write a balanced equation for the conversion of \(X\) to \(Y\).

The atomic masses of \({ }_{3}^{6} \mathrm{Li}\) and \({ }_{3}^{7} \mathrm{Li}\) are \(6.0151 \mathrm{amu}\) and 7.0160 amu, respectively. Calculate the natural abundances of these two isotopes. The average atomic mass of \(\mathrm{Li}\) is \(6.941 \mathrm{amu}\).

(a) A research chemist used a mass spectrometer to study the two isotopes of an element. Over time, she recorded a number of mass spectra of these isotopes. On analysis, she noticed that the ratio of the taller peak (the more abundant isotope) to the shorter peak (the less abundant isotope) gradually increased with time. Assuming that the mass spectrometer was functioning normally, what do you think was causing this change? (b) Mass spectrometry can be used to identify the formulas of molecules having small molecular masses. To illustrate this point, identify the molecule which most likely accounts for the observation of a peak in a mass spectrum at: 16 amu, \(17 \mathrm{amu}, 18 \mathrm{amu},\) and 64 amu. (c) Note that there are (among others) two likely molecules that would give rise to a peak at 44 amu, namely, \(\mathrm{C}_{3} \mathrm{H}_{8}\) and \(\mathrm{CO}_{2} .\) In such cases, a chemist might try to look for other pea generated when some of the molecules break apart in the spectrometer. For example, if a chemist sees a peak at 44 amu and also one at 15 amu, which molecule is producing the 44 amu peak? Why? (d) Using the following precise atomic masses: \({ }^{1} \mathrm{H}(1.00797 \mathrm{amu}),{ }^{12} \mathrm{C}(12.00000 \mathrm{amu}),\) and \({ }^{16} \mathrm{O}(15.99491 \mathrm{amu}),\) how precisely must the masses of \(\mathrm{C}_{3} \mathrm{H}_{8}\) and \(\mathrm{CO}_{2}\) be measured to distinguish between them? (e) Every year millions of dollars' worth of gold is stolen. In most cases the gold is melted down and shipped abroad. This way the gold retains its value while losing all means of identification. Gold is a highly unreactive metal that exists in nature in the uncombined form. During the mineralization of gold, that is, the formation of gold nuggets from microscopic gold particles, various elements such as cadmium (Cd), lead (Pb), and zinc (Zn) are incorporated into the nuggets. The amounts and types of the impurities or trace elements in gold vary according to the location where it was mined. Based on this knowledge, describe how you would identify the source of a piece of gold suspected of being stolen from Fort Knox, the federal gold depository.

Calculate the molecular mass or formula mass (in amu) of each of the following substances: (a) \(\mathrm{CH}_{4}\), (b) \(\mathrm{NO}_{2},\) (c) \(\mathrm{SO}_{3},\) (d) \(\mathrm{C}_{6} \mathrm{H}_{6}\), (e) NaI, (f) \(\mathrm{K}_{2} \mathrm{SO}_{4}\), (g) \(\mathrm{Ca}_{3}\left(\mathrm{PO}_{4}\right)_{2}\).

If we know the empirical formula of a compound, what additional information do we need to determine its molecular formula?
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