91Ó°ÊÓ

When a substance combusts, it combines with oxygen and releases energy. This energy is referred to as heat, and is often given in kilojoules (kJ). Enthalpy of combustion is a measure of this heat released per mole of substance combusted under constant pressure. In our problem, for every mole of carbon that turns into carbon dioxide (COâ‚‚), \(-393.5 \text{ kJ/mol}\) of heat is given off. The negative sign indicates that it is an exothermic reaction, meaning energy is exiting the system.

You can imagine it as a warm glow surrounding the reaction process. When calculating the heat released during a reaction, it's crucial to determine how many moles of the product are formed from the given mass, because the enthalpy value is always related to 1 mole of product.

In summary:

• Heat released indicates energy given off.
• Enthalpy of combustion is for 1 mole.
• Combustion reactions are exothermic (negative enthalpy).

The molar mass is the weight of one mole of a given substance. It's like finding out how much one dozen of apples weighs. For carbon dioxide (COâ‚‚), the molar mass helps us convert between the mass we have and the number of moles, which is essential for accurate calculations.

In COâ‚‚, we have one carbon atom and two oxygen atoms. - Carbon has an atomic mass of approximately 12.01 g/mol. - Oxygen has an atomic mass of about 16.00 g/mol

Combining these, we calculate the molar mass of COâ‚‚:
\[ \text{Molar mass of CO}_2 = 12.01 + 2 \times 16.00 = 44.01 \text{ g/mol} \]
This calculated molar mass allows you to determine how many moles are in any given mass of COâ‚‚. Without this number, it would be like trying to follow a recipe without knowing how many servings it makes!

To understand reactions quantitatively, it's crucial to calculate the number of moles from a given mass. This involves a simple division, using the formula:
\[ \text{moles} = \frac{\text{mass}}{\text{molar mass}} \]
By using this formula, you convert the mass of COâ‚‚ into moles, providing you with the quantity needed for further calculations, such as determining the heat released.

• Start by using the mass of COâ‚‚ given, which is 35.2 g.
• The molar mass of COâ‚‚, from our previous step, is 44.01 g/mol.

Now, perform the calculation:
\[ \text{moles of CO}_2 = \frac{35.2}{44.01} \approx 0.799 \text{ moles} \]
This number of moles tells you how much of the substance you are dealing with in terms of molecules rather than weight, opening doors to more meaningful and accurate chemical calculations!