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Question

A chemist measures the energy change 

Δ*H*

 during the following reaction:

CH4

*(g)*

+2O2

*(g)*

→CO2

*(g)*

+2H2O

*(l)*

=Δ*H*−882.kJ

Use the information to answer the following questions.


This reaction is...

endothermic.

exothermic.

Suppose 

28.2g

 of 

CH4

 react.

Will any heat be released or absorbed?

Yes, absorbed.

Yes, released.

No.

If you said heat *will* be released or absorbed in the second part of this question, calculate how *much* heat will be released or absorbed.

kJ

Be sure your answer has the correct number of significant digits.

### Step 1: Determine if the reaction is exothermic or endothermic

The enthalpy change \( \Delta H \) of the reaction is given as -882 kJ. The negative sign indicates that energy is being released from the system into the surroundings. Therefore, the reaction is **exothermic**.

### Answer: 
This reaction is **exothermic**.

---

### Step 2: Determine if heat is released or absorbed when 28.2 g of CH₄ reacts

Since the reaction is exothermic, heat will be **released** when CH₄ reacts. Therefore, when 28.2 g of CH₄ reacts, heat will be **released**.

### Answer: 
Yes, **released**.

---

### Step 3: Calculate how much heat will be released

We need to calculate how much heat will be released when 28.2 g of CH₄ reacts. First, let's find out how many moles of CH₄ correspond to 28.2 g.

- The molar mass of CH₄ (methane) is:
  \[
  12.01 \, (\text{C}) + 4 \times 1.008 \, (\text{H}) = 16.042 \, \text{g/mol}
  \]

- The number of moles of CH₄ in 28.2 g is:
  \[
  \text{moles of CH}_4 = \frac{28.2 \, \text{g}}{16.042 \, \text{g/mol}} = 1.758 \, \text{mol}
  \]

### Step 4: Use the given enthalpy change to find the heat released

The balanced reaction shows that 1 mole of CH₄ releases 882 kJ of heat. So, to find the heat released by 1.758 mol of CH₄, we multiply:
\[
\text{Heat released} = 1.758 \, \text{mol} \times \frac{-882 \, \text{kJ}}{1 \, \text{mol}} = -1551.2 \, \text{kJ}
\]

Thus, **1551 kJ** of heat will be released (rounded to the correct number of significant digits, 4).

### Answer: 
\( \text{Heat released} = 1551 \, \text{kJ} \)

---

Would you like further clarification or more details on any step?

---

### Related questions:
1. What is the difference between exothermic and endothermic reactions?
2. How do you determine if a reaction is exothermic based on \( \Delta H \)?
3. What are the units of molar enthalpy change \( \Delta H \)?
4. Why do we round our final answer to 4 significant digits in this calculation?
5. How would the enthalpy change differ if 50 g of CH₄ reacted instead of 28.2 g?

### Tip:
Always check the sign of \( \Delta H \). A negative value indicates that the reaction releases heat (exothermic), while a positive value means heat is absorbed (endothermic).

A chemist measures the energy change ΔH during the following reaction: CH4 (g) + 2O2 (g) → CO2 (g) + 2H2O (l) = ΔH −882.kJ. Use the information to answer the following questions. This reaction is... endothermic or exothermic? Suppose 28.2g of CH4 react. Will any heat be released or absorbed? If so, how much heat will be released or absorbed? Be sure your answer has the correct number of significant digits.

Learn how to calculate the amount of heat released when 28.2g of CH4 reacts in an exothermic reaction with ΔH = -882 kJ. This problem involves stoichiometric calculations and applying significant figures to determine the correct heat release. Suitable for Grades 10-12 students studying thermodynamics.

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