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Chapter 4 SABIS Grade 10 Part 4

STP, Volume Ratios, Energy in Reactions, and Limiting Reagents

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✅Lesson 19: ✅
STP, Volume Ratios, Energy in Reactions, and Limiting Reagents

Hello learners! 🌞🎒 Today's chemistry class is going to be a thrilling ride as we explore concepts like Standard Temperature and Pressure (STP), stoichiometric calculations, and limiting reagents. Buckle up and get ready! 🚀🔬💡

Prerequisite Material Quiz 📚🧠

  1. What does STP stand for?

  2. What are the conditions for STP?

  3. True or False: At STP, 1.00 mole of any gas occupies 22.4 dm³.

  4. How much percentage of air is oxygen gas by volume?

  5. What is a limiting reagent in a chemical reaction?

  6. Can the volume ratio at STP be used for any given reaction equation?

  7. True or False: The limiting reagent determines how much of the other reactants will be consumed in a chemical reaction.

  8. Can we write an equation including the energy required or released?

  9. True or False: A limiting reagent gets completely used up in a chemical reaction.

  10. Can we solve problems using the volume ratio?

(Answers at the end of the lesson)

Explanation: STP, Volume Ratios, Energy in Reactions, and Limiting Reagents 🧐👩‍🔬

Standard Temperature and Pressure (STP)

STP is a common set of conditions for gases defined as 0 degrees Celsius and 1.00 atmosphere pressure. Under these conditions, any gas will have a volume of 22.4 dm³ per mole.

Volume Ratios

In gas reactions at STP, the volumes of gases involved can be directly related to the coefficients in the balanced equation. These are the volume ratios.

Energy in Reactions

Chemical reactions either absorb or release energy. We can represent this energy change in the chemical equation.

Limiting Reagents

In a chemical reaction, the limiting reagent is the substance that gets completely consumed and determines the maximum amount of product that can be formed.

Examples 🌍🔬🔎

  • STP and volume ratios: In the reaction 2H₂(g) + O₂(g) → 2H₂O(g), the volume ratio of hydrogen to oxygen to water vapor is 2:1:2. If we start with 44.8 dm³ of hydrogen gas at STP, we would expect to produce 44.8 dm³ of water vapor, assuming oxygen is not the limiting reagent.

  • Energy in reactions: In the combustion of methane (exothermic reaction), energy is released: CH₄(g) + 2O₂(g) → CO₂(g) + 2H₂O(g) + energy.

  • Limiting reagents: If we react 4 moles of hydrogen gas with 1 mole of nitrogen gas according to the equation N₂(g) + 3H₂(g) → 2NH₃(g), hydrogen is the limiting reagent. It will be completely consumed and determine the maximum amount of ammonia that can be produced (2 moles).

Post-lesson MCQs 📝✅

  1. True or False: At STP, all gases have the same volume per mole.

  2. What is the volume ratio of hydrogen to oxygen in the balanced equation for the formation of water?

  3. Can energy be a product in a chemical reaction?

  4. True or False: The limiting reagent in a reaction is always the reactant with the smallest amount of moles.

  5. How do we determine the mass of the excess reagent left in a reaction?

(Answers at the end of the lesson) Answers

Prerequisite Material Quiz:

  1. Standard Temperature and Pressure,

  2. 0 degrees Celsius and 1.00 atmosphere pressure,

  3. True,

  4. 20%,

  5. The substance that gets completely consumed in a reaction,

  6. Yes,

  7. True,

  8. Yes,

  9. True,

  10. Yes.

Post-lesson MCQs:

  1. True,

  2. 2:1,

  3. Yes, energy can be a product in exothermic reactions,

  4. False, the limiting reagent is the substance that is completely consumed in a reaction, not necessarily the one with the smallest amount of moles,

  5. By subtracting the amount of the reagent that reacted from the total amount initially present.

Complete the Questions:

  1. The volume ratio at STP for a given reaction equation is directly related to the coefficients of the gases in the balanced equation.

  2. An example of an endothermic reaction is the thermal decomposition of calcium carbonate: CaCO₃(s) + energy → CaO(s) + CO₂(g).

  3. The volume of 2 moles of nitrogen gas at STP is 2 moles × 22.4 dm³/mole = 44.8 dm³.

  4. Stoichiometric calculations involve using the coefficients in a balanced equation to calculate quantities of reactants or products. It can involve mole, mass, volume, or energy ratios.

  5. The limiting reagent is determined by comparing the amount of products each reactant could produce if it were completely consumed. The reactant that produces the least amount of product is the limiting reagent.


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