3. Given a chemical reaction and H associated with the reaction: stoichiometry and limiting reactant problem involving gases.

Why would we need delta H for a stoichimetry or limiting reactant problem? And can i get an example pleasE?

The value of ΔH (enthalpy change) is useful in stoichiometry and limiting reactant problems involving gases because it allows for the calculation of the amount of heat energy released or absorbed during a chemical reaction. This information is crucial for determining the quantities of reactants and products involved.

Consider the following example:

Example:

The reaction between hydrogen gas (H2) and oxygen gas (O2) to form water (H2O) is given by the balanced chemical equation:

2H2(g) + O2(g) → 2H2O(g) ΔH = -483.7 kJ

Suppose we have 10 moles of hydrogen gas and 8 moles of oxygen gas. We can use ΔH to determine which reactant is the limiting reactant and the maximum amount of water that can be produced.

1. Calculate the theoretical yield of water for each reactant:

For hydrogen gas (H2):
According to the balanced equation, 1 mole of O2 reacts with 2 moles of H2 to produce 2 moles of H2O.

Therefore, the theoretical yield of water from 10 moles of H2 is:
(10 mol H2) x (2 mol H2O / 2 mol H2) = 10 moles of H2O

For oxygen gas (O2):
According to the balanced equation, 1 mole of O2 reacts with 2 moles of H2 to produce 2 moles of H2O.

Therefore, the theoretical yield of water from 8 moles of O2 is:
(8 mol O2) x (2 mol H2O / 1 mol O2) = 16 moles of H2O

2. Determine the limiting reactant:
The limiting reactant is the one that produces the least amount of product. In this case, hydrogen gas (H2) produces a theoretical yield of 10 moles of water, while oxygen gas (O2) produces a theoretical yield of 16 moles of water. Since we only have 10 moles of H2 available, it is the limiting reactant.

3. Calculate the actual yield of water:
The actual yield of water is the amount obtained in the reaction, which is limited by the amount of the limiting reactant. In this case, the actual yield of water would be 10 moles, as determined by the amount of H2 available.

Therefore, in this example, the ΔH value allowed us to determine the limiting reactant (H2) and the maximum amount of water (10 moles) that can be produced.

The value of ∆H (delta H), which represents the change in enthalpy, is important in stoichiometry and limiting reactant problems because it allows us to calculate how much heat is released or absorbed during a reaction. This information is crucial for determining the quantities of reactants and products involved in the reaction.

To explain further, stoichiometry is the study of the quantitative relationships between reactants and products in a chemical reaction. It involves using balanced chemical equations and molar ratios to calculate the amounts of substances before and after the reaction.

The limiting reactant problem, on the other hand, arises when there are two or more reactants involved in a reaction, and one of them is consumed completely before the others. The limiting reactant is the one that determines the maximum amount of product that can be formed. To find the limiting reactant, we need the stoichiometry of the reaction and the molar quantities of the reactants.

Here's an example to illustrate how ∆H is used in stoichiometry and limiting reactant problems involving gases:

Suppose we have the following balanced chemical equation representing the combustion of methane (CH4) gas:

CH4(g) + 2O2(g) → CO2(g) + 2H2O(g)

Let's assume the value of ∆H for this reaction is -890 kJ/mol of methane consumed.

Now, if we have 10 moles of methane and excess oxygen, we can use stoichiometry to calculate the amount of heat released:

∆H = -890 kJ/mol CH4 (from the given value)
∆H = -890 kJ/mol x 10 mol CH4 (using stoichiometry)
∆H = -8900 kJ

Therefore, the combustion of 10 moles of methane would release 8900 kJ of heat.

In a limiting reactant problem, let's say we only have 5 moles of methane and 7 moles of oxygen. To determine the limiting reactant and the maximum amount of product formed, we compare the moles of reactants to the stoichiometric ratios:

Moles of methane: 5 mol
Moles of oxygen: 7 mol

Using the balanced equation, we can see that 1 mole of methane reacts with 2 moles of oxygen. Therefore, the ratio of moles of methane to oxygen should be 1:2. However, in this case, we have a 1:7 ratio, which means that the methane is the limiting reactant.

We can calculate the maximum moles of product (CO2) formed using the limiting reactant (methane) and the stoichiometric ratio:

Moles of methane: 5 mol
Molar ratio of methane:CO2 = 1:1 (from the balanced equation)

Therefore, the maximum moles of CO2 formed would also be 5 mol.

I hope this example clarifies why ∆H is necessary and how it is used in stoichiometry and limiting reactant problems involving gases!