Bomb Calorimeter & Methane Combustion: A Chemistry Problem

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Hey guys! Let's dive into a classic chemistry problem involving a bomb calorimeter and the complete combustion of methane. We'll break down the concepts, calculations, and correct statements. It might sound intimidating, but trust me, we'll make it easy to understand. So, grab your calculators, and let's get started!

Understanding the Bomb Calorimeter

First, let's talk about what a bomb calorimeter actually is. Think of it as a super-insulated container specifically designed to measure the heat released or absorbed during a chemical reaction at constant volume. It's like a tiny, controlled explosion chamber surrounded by water. The reaction happens inside the "bomb," and the heat produced is absorbed by the water surrounding it. By carefully measuring the temperature change of the water, we can figure out how much heat was involved in the reaction.

The key components of a bomb calorimeter are:

  • The Bomb: A strong, sealed container where the reaction takes place.
  • Water Bath: The water surrounding the bomb, which absorbs the heat.
  • Thermometer: Used to precisely measure the temperature change of the water.
  • Stirrer: Ensures the water is evenly heated.

Bomb calorimeters are incredibly useful for determining the heat of combustion of various substances. The "heat of combustion" is simply the amount of heat released when one mole of a substance is completely burned. This information is crucial in many fields, from understanding the energy content of fuels to designing chemical processes.

Why is it called a "bomb" calorimeter? Well, the reactions inside the calorimeter often involve combustions that create a high pressure environment inside the bomb. This high pressure ensures a complete reaction of the materials.

Now, let's consider the problem at hand:

We have 0.5 g of methane (CH4) being completely burned inside the bomb calorimeter. The temperature of 500 g of water rises from 20°C to 22.5°C. The specific heat capacity of water is 4.18 J/g°C.

Analyzing the Given Statements

The problem presents us with statements, and our job is to determine which ones are correct based on the given information. Let's break down each statement:

Statement 1: Kalor yang diserap air = 500 x 4,18 x 2,5 = 5225 J

This statement deals with the heat absorbed by the water. Remember the formula for calculating heat (q) absorbed or released:

q = m * c * ΔT

Where:

  • q = heat absorbed or released (in Joules)
  • m = mass (in grams)
  • c = specific heat capacity (in J/g°C)
  • ΔT = change in temperature (in °C)

Plugging in the values:

q = 500 g * 4.18 J/g°C * (22.5°C - 20°C) q = 500 g * 4.18 J/g°C * 2.5°C q = 5225 J

So, Statement 1 is correct! The heat absorbed by the water is indeed 5225 J.

Statement 2: Jumlah mol metana = ?

This statement requires us to calculate the number of moles of methane (CH4) that were burned. To do this, we need the molar mass of methane.

The molar mass of CH4 is calculated as follows:

  • Molar mass of C = 12.01 g/mol
  • Molar mass of H = 1.008 g/mol
  • Molar mass of CH4 = 12.01 + (4 * 1.008) = 16.042 g/mol

Now, we can calculate the number of moles using the formula:

Moles = Mass / Molar mass

Moles of CH4 = 0.5 g / 16.042 g/mol Moles of CH4 ≈ 0.0312 mol

Putting It All Together

So far, we've confirmed that Statement 1 is correct and calculated the number of moles of methane in Statement 2.

Statement 1: Kalor yang diserap air = 500 x 4,18 x 2,5 = 5225 J

This statement is correct because we used the formula q = m * c * ΔT to accurately calculate the heat absorbed by the water.

Statement 2: Jumlah mol metana = approximately 0.0312 mol

To determine the number of moles of methane (CH4), we utilize the formula:

Number of Moles = Mass / Molar Mass

Given:

  • Mass of CH4 = 0.5 g
  • Molar Mass of CH4 ≈ 16.042 g/mol

Number of Moles of CH4 = 0.5 g / 16.042 g/mol ≈ 0.0312 moles

Therefore, the amount of methane is approximately 0.0312 mol.

Additional Considerations

Now, let's think about what this information tells us. The heat absorbed by the water (5225 J) is equal to the heat released by the combustion of 0.0312 moles of methane.

We can calculate the heat of combustion per mole of methane:

Heat of combustion per mole = Heat released / Moles Heat of combustion per mole = 5225 J / 0.0312 mol Heat of combustion per mole ≈ 167468 J/mol or 167.468 kJ/mol

This value represents the amount of heat released when one mole of methane is completely burned under constant volume conditions in the bomb calorimeter. This information can be compared to standard values to assess the accuracy of the experiment or to understand the energy content of methane as a fuel.

Common Mistakes to Avoid

When solving calorimetry problems, there are a few common pitfalls to watch out for:

  • Forgetting Units: Always include units in your calculations. This helps prevent errors and ensures your answer is in the correct units.
  • Incorrectly Calculating ΔT: Make sure to subtract the initial temperature from the final temperature (ΔT = T_final - T_initial).
  • Using the Wrong Specific Heat Capacity: Double-check that you're using the correct specific heat capacity for the substance involved (in this case, water).
  • Ignoring the Sign of q: Remember that a negative q indicates heat released (exothermic reaction), while a positive q indicates heat absorbed (endothermic reaction).

Conclusion

So, there you have it! We've successfully analyzed a bomb calorimeter problem involving methane combustion. We calculated the heat absorbed by the water, the number of moles of methane, and even estimated the heat of combustion per mole of methane. Remember to pay attention to the details, use the correct formulas, and watch out for those common mistakes. Keep practicing, and you'll become a calorimetry pro in no time!

Hopefully, this explanation was helpful, and you now have a better understanding of bomb calorimeters and combustion reactions. Keep exploring, and happy learning!