At constant pressure, which of these systems do work on the surroundings? Check all that apply.

A(s) + 2B(g) ---> C(g)
2A(g) + B(g) ---> 4C(g)
A(g) + 2B(g) ---> 2C(g)
A(s) + B(s) ---> C(g)

If # mol gets larger, that's an expansion, and the system does work on the surroundings. If # mol gets smaller, that's a decrease in volume, and the surroundings do work on the system.

Watch out for those solids. They are not gases and don't count when counting moles.

Thank you so very much~! <3

In a chemical reaction, work is defined as the energy transferred due to the volume change of the system against an external pressure. If the volume of the system increases, work is done on the surroundings.

Let's analyze each reaction to determine if work is done on the surroundings:

1. A(s) + 2B(g) ---> C(g)
- In this reaction, there are more moles of gas on the product side compared to the reactant side. As a result, the volume of the system increases, and work is done on the surroundings.

2. 2A(g) + B(g) ---> 4C(g)
- In this reaction, the number of gas molecules remains the same on both sides of the equation. Therefore, there is no change in volume, and no work is done on the surroundings.

3. A(g) + 2B(g) ---> 2C(g)
- Similar to the first reaction, the number of moles of gas on the product side is higher than the reactant side. The volume of the system increases, and work is done on the surroundings.

4. A(s) + B(s) ---> C(g)
- In this reaction, all reactants and products are in condensed phases (solid or liquid). There is no change in volume, and hence, no work is done on the surroundings.

Therefore, the reactions that do work on the surroundings are:
1. A(s) + 2B(g) ---> C(g)
3. A(g) + 2B(g) ---> 2C(g)

To determine which of these systems do work on the surroundings at constant pressure, we need to first understand the concept of work in chemistry.

Work is defined as the energy transferred as a result of a force acting through a distance. In the context of chemical reactions, work can be done on the surroundings or by the surroundings depending on the type of system and the direction of the reaction.

For a reaction to do work on the surroundings, the volume of the system must change against an external pressure. This occurs when gaseous molecules are produced and the gas expands against the external pressure.

Let's analyze each reaction and check which ones do work on the surroundings:

A(s) + 2B(g) ---> C(g):
In this reaction, a solid reacts with a gas to form a gas. Since there is an increase in the total number of moles of gas, the volume of the system increases. Therefore, this reaction does work on the surroundings.

2A(g) + B(g) ---> 4C(g):
In this reaction, all species are gases. Although the number of moles increases from 3 to 4, the total volume of the system doesn't change. This means that the gas doesn't expand against the external pressure, so no work is done on the surroundings in this case.

A(g) + 2B(g) ---> 2C(g):
Similar to the previous reaction, all species are gases, but the total number of moles remains the same. As a result, no work is done on the surroundings in this case.

A(s) + B(s) ---> C(g):
In this reaction, both reactants are solids and one product is a gas. Since there is no gaseous expansion, no work is done on the surroundings in this reaction.

In summary, the reactions that do work on the surroundings at constant pressure are:

- A(s) + 2B(g) ---> C(g)

Note: It's important to consider the stoichiometry of the reaction and determine if the total volume changes due to the formation or consumption of gaseous species.