Calculate the amount of heat needed to boil 167.g of hexane (C6H14), beginning from a temperature of −7.4°C. Be sure your answer has a unit symbol and the correct number of significant digits.

To solve this problem, we need to consider two steps:

1. Heating the hexane from -7.4°C to its boiling point (69°C)
2. Boiling the hexane at 69°C

First, we need to find the amount of heat needed to raise the temperature of hexane from -7.4°C to 69°C. We can use the formula q = mcΔT, where q is the heat energy, m is the mass, c is the specific heat capacity, and ΔT is the change in temperature.

The specific heat capacity of hexane is 2.27 J/g°C, the mass is 167 g, and the change in temperature is 69°C - (-7.4°C) = 76.4°C.

So, q1 = (167 g)(2.27 J/g°C)(76.4°C) = 28800 J

Next, we need to find the amount of heat needed to boil the hexane at 69°C. We can use the formula q = mL, where q is the heat energy, m is the mass, and L is the heat of vaporization.

The heat of vaporization of hexane is 30.1 kJ/mol. But first, we need to convert the mass of hexane to moles. The molar mass of hexane is about 86.18 g/mol.

So, moles of hexane = 167 g / 86.18 g/mol = 1.94 mol

Then, q2 = (1.94 mol)(30.1 kJ/mol) = 58.4 kJ = 58400 J

Finally, we add the two amounts of heat together to find the total heat needed.

q_total = q1 + q2 = 28800 J + 58400 J = 87200 J

So, the amount of heat needed to boil 167 g of hexane, beginning from a temperature of -7.4°C, is 87200 J.