Question

3. Given the following equation: CH4(g) + 2 O2(g) > CO2(g) + 2 H2O(l) AH = -890.4 kJ a. How much energy is given off when 5.00 moles of CH4 are burned? And How much energy is released when 85.6 grams of CH4 are burned?

Answer 1

-4452 kJ is given off from 5.00 moles of CH4.

-4763.64 kJ is given off from 85.6 grams of CH4.

Step-by-step explanation:

First, let's write the equation:

`CH_4+2O_2\rightarrow CO_2+2H_2O,\text{ }\Delta H=-890.4\text{ kJ.}`

a. We want to know how much energy is given off when 5.00 moles of CH4 are burned, so if we 'multiply' all the coefficients by 5.00 moles, the enthalpy change (ΔH) will also be multiplied by 5.00, so we're going to have:

`\Delta H\cdot5=-890.4\text{ kJ}\cdot5=-4452\text{ kJ.}`

-4452 kJ is given off from 5.00 moles of CH4.

Now, to find how much energy is released when 85.6 g of CH4 are burned, we have to find the number of moles using the molar mass of CH4 which is 16 g/mol (you can calculate the molar mass of a compound using the periodic table). The conversion will look like this:

`85.6\text{ g CH}_4\cdot\frac{1\text{ mol CH}_4}{16\text{ g CH}_4}=5.35\text{ moles CH}_4.`

We have 5.35 moles of CH4, so we have to follow the same steps that we did before:

`\Delta H\cdot5.35=-890.4k\text{ kJ}\cdot5.35=-4763.64\text{ kJ.}`

-4763.64 kJ is given off from 85.6 grams of CH4.