Question

1. what is the enthalpy change when 83.5 g of methane combusts? i can determine the enthalpy change for one mole of a substance. youve got it! next steps:

Explanation:

Step1: Calculate the molar mass of methane ($CH_4$)

The molar mass of $C$ is $12.01\ g/mol$ and of $H$ is $1.008\ g/mol$. For $CH_4$, $M=(12.01 + 4\times1.008)\ g/mol=16.042\ g/mol$.

Step2: Calculate the number of moles of methane

Using the formula $n=\frac{m}{M}$, where $m = 83.5\ g$ and $M = 16.042\ g/mol$. So $n=\frac{83.5}{16.042}\ mol\approx5.205\ mol$.

Step3: Calculate the enthalpy change

Given $\Delta H_{comb}=- 890.8\ kJ/mol$. Using the formula $\Delta H=n\times\Delta H_{comb}$. Substitute $n = 5.205\ mol$ and $\Delta H_{comb}=-890.8\ kJ/mol$. Then $\Delta H=5.205\times(- 890.8)\ kJ\approx - 4637\ kJ$.

Answer:

The enthalpy change is approximately $-4637\ kJ$.