Question

question 3
1 pts
a reaction occurs, resulting in an increase in
the volume of a system. work is done
---------
by the system on the surroundings
by transfer of heat
by the surroundings on the system
by the surroundings on the universe

question 4
1 pts
propane (c3h8) has a heat of combustion of
-2220.0 kj/mol. how much heat is
released if 35.0 g of propane are
combusted in excess oxygen?
2220 kj
1760 kj
875 kj
2800 kj

Explanation:

Question 3

When the volume of a system increases, the system expands. In thermodynamics, when a system expands, it does work on the surroundings. Heat transfer is a different mode of energy transfer (not related to volume - change work in this context). Work done by the surroundings on the system would correspond to compression (volume decrease). And work done by the surroundings on the universe is not a relevant concept in the context of the first - law of thermodynamics for a system - surroundings interaction.

Step1: Calculate the molar mass of propane

The molar mass of \(C_3H_8\): \(M=(3\times12.01 + 8\times1.008)\space g/mol=(36.03+8.064)\space g/mol = 44.094\space g/mol\)

Step2: Calculate the number of moles of propane

The number of moles \(n=\frac{m}{M}\), where \(m = 35.0\space g\) and \(M = 44.094\space g/mol\). So \(n=\frac{35.0\space g}{44.094\space g/mol}\approx0.794\space mol\)

Step3: Calculate the heat released

Given that the heat of combustion is \(\Delta H=- 2220.0\space kJ/mol\). The heat released \(q=n\times|\Delta H|\) (we take the absolute value of \(\Delta H\) for the amount of heat released). So \(q = 0.794\space mol\times2220.0\space kJ/mol\approx1760\space kJ\)

Answer:

by the system on the surroundings

Question 4