Acetylene \(\left(\mathrm{C}_{2} \mathrm{H}_{2}\right)\) and hydrogen fluoride (HF) react to give difluoroethane: $$ \mathrm{C}_{2} \mathrm{H}_{2}(g)+2 \mathrm{HF}(g) \longrightarrow \mathrm{C}_{2} \mathrm{H}_{4} \mathrm{~F}_{2}(g) $$ When \(1.0 \mathrm{~mol}\) of \(\mathrm{C}_{2} \mathrm{H}_{2}\) and \(5.0 \mathrm{~mol}\) of \(\mathrm{HF}\) are reacted in a 10.0-L flask, what will be the pressure in the flask at \(0^{\circ} \mathrm{C}\) when the reaction is complete?

Stoichiometry is the calculation of reactants and products in chemical reactions. It is based on the balanced chemical equation, which shows the relationship between the quantities of reactants and products. To solve stoichiometry problems, follow these steps:

• Balance the chemical equation to get the correct ratio of reactants to products.
• Convert quantities of known substances into moles (using molar masses if necessary).
• Use the balanced equation to set up mole ratios and solve for the unknown quantities.

In our example, the balanced equation is: \[ \mathrm{C}_{2} \mathrm{H}_{2}(g)+2 \mathrm{HF}(g) \longrightarrow \mathrm{C}_{2} \mathrm{H}_{4} \mathrm{~F}_{2}(g) \] This tells us that 1 mole of \(\mathrm{C}_{2}\mathrm{H}_{2} \) reacts with 2 moles of \(\mathrm{HF}\) to produce 1 mole of \(\mathrm{C}_{2} \mathrm{H}_{4} \mathrm{~F}_{2} \). Make sure to use these coefficients in calculations.

In chemical reactions, the limiting reactant is the substance that is completely consumed first, limiting the amount of product that can be formed. To identify the limiting reactant:

• Calculate the moles of each reactant available.
• Use the stoichiometric coefficients to determine how much of each reactant is needed to react completely.
• Compare the amount needed to the amount available to see which reactant will run out first.

In the provided exercise, we determined that 1 mole of \(\mathrm{C}_{2} \mathrm{H}_{2} \) reacts with 2 moles of \(\mathrm{HF} \). Given 1 mole of \(\mathrm{C}_{2} \mathrm{H}_{2} \) and 5 moles of \(\mathrm{HF} \), the acetylene is the limiting reactant because it requires only 2 moles of HF for complete reaction, and we have more than enough HF.

The Ideal Gas Law is a fundamental equation in chemistry that describes the behavior of ideal gases. It is written as: \[ PV = nRT \]

• \(P \) is the pressure of the gas.
• \(V \) is the volume of the gas.
• \(n \) is the number of moles of the gas.
• \(R \) is the ideal gas constant \(0.0821 \frac{L\text{atm}}{K\text{mol}} \).
• \(T \) is the temperature in Kelvin.

To find the pressure when the reaction is complete, we substitute the values into the Ideal Gas Law equation. For the given problem, the volume is 10.0 L, the total moles of gas is 4, the temperature is 0°C (which is 273 K), and the gas constant is \(0.0821 \frac{L\text{atm}}{K\text{mol}} \). Rewriting the equation for pressure: \[ P = \frac{nRT}{V} = \frac{(4 \text{ mols})(0.0821 \frac{L\text{atm}}{K\text{mol}})(273K)}{(10.0 \text{ L})} \approx 8.98 \text{ atm} \] So, the pressure in the flask when the reaction is complete is approximately 8.98 atm.

A chemical reaction involves the transformation of reactants into products. Indicators of a chemical reaction include color change, temperature change, gas production, and precipitate formation. To understand chemical reactions, keep these points in mind:

• Reactants are substances that start a reaction, while products are substances that are produced.
• A balanced chemical equation follows the law of conservation of mass, meaning the number of atoms of each element must be the same on both sides.
• Chemists use balanced equations to predict the amounts of products and reactants involved.

In our example, the equation shows the reactants \(\mathrm{C}_{2} \mathrm{H}_{2} \) and \(\mathrm{HF} \), while \(\mathrm{C}_{2} \mathrm{H}_{4} \mathrm{~F}_{2} \) is the product. The balanced equation ensures that the same amount of each atom is present before and after the reaction.

Gas pressure is the force exerted by gas molecules when they collide with the walls of their container. It is influenced by several factors:

• Number of gas molecules: More molecules result in higher pressure.
• Temperature: Higher temperatures increase the kinetic energy of molecules, leading to more frequent collisions and higher pressure.
• Volume of the container: A smaller volume leads to more collisions and higher pressure.

The Ideal Gas Law \(PV = nRT \) connects these factors to calculate gas pressure. For example, in the exercise, we calculated the pressure to be approximately 8.98 atm after completing the reaction by considering the total moles of gas, the temperature, and the volume of the container.