Question

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. ○ exothermic. suppose 98.9 g 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. be sure your answer has the correct number of significant digits. kj

Explanation:

First Question: Determine Reaction Type

Step1: Recall Enthalpy Sign Meaning

For a reaction, $\Delta H < 0$ means heat is released (exothermic), $\Delta H > 0$ means heat is absorbed (endothermic). Here, $\Delta H = -882\ \text{kJ} < 0$.

Step2: Classify Reaction

Since $\Delta H$ is negative, the reaction releases heat, so it's exothermic.

Second Question: Heat Release/Absorption

Step1: Reaction Nature

The reaction is exothermic (from first part), so when $\ce{CH4}$ reacts, heat is released.

Step2: Confirm Based on Reaction

As the reaction has negative $\Delta H$ (exothermic), reacting $\ce{CH4}$ will release heat. So answer is "Yes, released".

Third Question: Calculate Heat Released

Step1: Molar Mass of $\ce{CH4}$

Molar mass of $\ce{C}$ is $12.01\ \text{g/mol}$, $\ce{H}$ is $1.008\ \text{g/mol}$. So $M(\ce{CH4}) = 12.01 + 4\times1.008 = 16.042\ \text{g/mol}$.

Step2: Moles of $\ce{CH4}$

Moles $n = \frac{\text{mass}}{\text{molar mass}} = \frac{98.9\ \text{g}}{16.042\ \text{g/mol}} \approx 6.165\ \text{mol}$.

Step3: Heat Released per Mole

From reaction, 1 mol $\ce{CH4}$ releases $882\ \text{kJ}$ (since $\Delta H$ is -882 kJ, magnitude is heat released).

Step4: Total Heat Released

Heat $q = n \times 882\ \text{kJ/mol} = 6.165\ \text{mol} \times 882\ \text{kJ/mol} \approx 5430\ \text{kJ}$ (or $5.43\times10^3\ \text{kJ}$, considering significant digits: 98.9 has 3, 882 has 3, so result should have 3 significant digits).

Answer:

s:

1. This reaction is...: exothermic.
2. Suppose 98.9 g of $\ce{CH4}$ react. Will any heat be released or absorbed?: Yes, released.
3. Heat released: $\boxed{5430}$ (or $5.43\times10^3$) kJ.