Limiting Reagents

What is a limiting reagent in a chemical reaction?

• A catalyst that speeds up the reaction

• The product formed in the reaction

• The reactant that is available in excess

• The reactant that is completely used up first, stopping the reaction

Answer explanation

The reactant that is completely used up first, stopping the reaction

What is the result when 2.40 g of Mg reacts with 10.0 g of O2?

The unbalanced reaction is Mg + O₂ --> MgO

• Both react completely

• No reaction occurs

• Mg is the limiting reagent

• O2 is the limiting reagent

Answer explanation

Mg is the limiting reagent because it will be completely consumed before all the O2 reacts, resulting in excess O2.

Tags

NGSS.HS-PS1-7

How much excess O2 is left when 2.40 g of Mg reacts with 10.0 g of O₂?

The reaction is 2Mg + O₂ --> 2MgO

• 2.40 g O2

• 8.42 g O2

• 1.58 g O2

• 10.0 g O2

Answer explanation

To find the excess O2, calculate the moles of Mg and O2, determine the limiting reactant (Mg), find the moles of O2 reacted, and subtract from the initial moles of O2 to get 8.42 g of excess O2.

Tags

NGSS.HS-PS1-7

What is the correct balanced chemical equation for the oxidation of magnesium?

• 2 Mg + 2 O2 -> 2 MgO

• Mg + 2 O2 -> MgO

• 2 Mg + O2 -> 2 MgO

• Mg + O2 -> MgO

Answer explanation

The correct balanced chemical equation for the oxidation of magnesium is 2 Mg + O2 -> 2 MgO, as it shows the correct stoichiometry of the reaction.

Tags

NGSS.HS-PS1-7

How much MgO is produced when 2.40 g of Mg reacts with 10.0 g of O2?

• 3.98 g MgO

• 2.40 g MgO

• 25.2 g MgO

• 10.0 g MgO

Answer explanation

To find the amount of MgO produced, calculate the moles of Mg and O2, determine the limiting reactant, then use stoichiometry to find the mass of MgO. The correct answer is 3.98 g MgO.

Tags

NGSS.HS-PS1-7

What happens when the reactants are not mixed in the correct stoichiometric proportions?

• One of the reactants will be entirely consumed while another will be left over

• The reaction will not occur

• The reaction will produce more products

• All reactants will be used up completely

Answer explanation

One of the reactants will be entirely consumed while another will be left over

Tags

NGSS.HS-PS1-7

The limiting reactant

• slows the reaction down

• is used up first

• is the reactant that is left over

• controls the speed of the reaction

Answer explanation

The limiting reactant is used up first, as it determines the maximum amount of product that can be formed in a reaction.

Identify the limiting reagent when 6.00 g HCl combines with 5.00 g Mg to form MgCl₂.
 
Mg +  2HCl --> MgCl₂  +  H₂   
 

• Mg

• H2

• MgCl2

• HCl

Answer explanation

HCl is the limiting reagent because it will be completely consumed before Mg in the reaction, based on the given masses.

Tags

NGSS.HS-PS1-7

If you are converting from grams of substance A to grams of substance B, drag the correct order of the conversion process:

​ (a)   ---> ​ (b)   ---> ​ (c)   ---> ​ (d)  

• Grams A

• Moles A

• Moles B

• Grams B

Answer explanation

To convert from grams of substance A to grams of substance B, the correct order is: Grams A -> Moles A -> Moles B -> Grams B.

Tags

NGSS.HS-PS1-7

Theoretical yield = 73g
Actual yield = 62g
Calculate the percent yield.

• 1.16%
• 116%
• 85%
• 76%

Tags

NGSS.HS-PS1-7