During the combustion of 5.00 g of octane, C8H18, 239.5 kcal is released.
a) What is the sign of (delta)H for this reaction?
b) How much energy is released by the combustion of 1.00 mol of C8H18
a) negative
b) 1.00 mol C8H18 x 114.26g C8H18/1mol x 239.5 kcal/5.00g C8H18 = 5.47x10^3 kcal or 5473.054 kcal
yeah
a) The sign of ΔH for this reaction is negative (-239.5 kcal). Since energy is being released, the reaction is exothermic.
b) To calculate the energy released by the combustion of 1.00 mol of C8H18, we first need to find the molar mass of octane (C8H18).
The molar mass for octane can be calculated by adding up the atomic masses of each element in the compound:
(Carbon: 12.01 g/mol * 8 atoms) + (Hydrogen: 1.008 g/mol * 18 atoms)
= 96.08 g/mol + 18.14 g/mol
= 114.22 g/mol
Since the given energy is for 5.00 g of octane, we can calculate the moles of octane in 5.00 g using the molar mass:
5.00 g / 114.22 g/mol = 0.0438 mol
Now, we can use this value to calculate the energy released by the combustion of 1.00 mol of octane:
(239.5 kcal / 0.0438 mol) * 1.00 mol = 5468.4 kcal/mol
Therefore, the energy released by the combustion of 1.00 mol of C8H18 is 5468.4 kcal.
To answer this question, we need to understand the concept of enthalpy change in a reaction and how it relates to the given information.
a) The sign of ΔH (enthalpy change) for this reaction can be determined by observing whether energy is released or absorbed during the reaction. Since 239.5 kcal of energy is released during the combustion of octane, ΔH is negative. This is because energy is being released from the system, resulting in a decrease in enthalpy, hence the negative sign.
b) To determine the amount of energy released by the combustion of 1.00 mol of C8H18, we need to use the given amount of energy released for 5.00 g of octane. Here's how we can calculate it:
1. Find the molar mass of octane (C8H18):
C = 12.01 g/mol (carbon atomic mass)
H = 1.01 g/mol (hydrogen atomic mass)
Thus, the molar mass of C8H18 = (8 × C) + (18 × H) = (8 × 12.01) + (18 × 1.01) = 114.23 g/mol
2. Calculate the number of moles of octane in 5.00 g:
Number of moles = mass / molar mass = 5.00 g / 114.23 g/mol ≈ 0.0438 mol
3. Use the given amount of energy released for 5.00 g of octane to calculate the energy released for 1 mol of octane:
Energy released by 1 mol = (Energy released for 5.00 g / 0.0438 mol) × 1 mol
Energy released by 1 mol = 239.5 kcal / 0.0438 mol ≈ 5475 kcal/mol
Therefore, the combustion of 1.00 mol of C8H18 releases approximately 5475 kcal of energy.