Given:
- Number of moles (n) = 0.75 mol
- Initial volume (V1) = 15 L
- Final volume (V2) = 25 L
- Pressure (P) = 1 atm

Formula:
The work done by expansion of a gas can be calculated using the formula:

Work (W) = -PΔV

Where:
- W is the work done
- P is the pressure
- ΔV is the change in volume

Calculations:
1. Calculate the change in volume:
ΔV = V2 - V1
= 25 L - 15 L
= 10 L

2. Substitute the values into the formula to calculate the work done:
W = -PΔV
= -(1 atm)(10 L)
= -10 atm·L

Explanation:
The work done by the expansion of a gas is given by the formula W = -PΔV, where P is the pressure and ΔV is the change in volume. In this case, the initial volume is 15 L and the final volume is 25 L, resulting in a change in volume of 10 L. The pressure is given as 1 atm.

Substituting these values into the formula, we can calculate the work done as -10 atm·L. The negative sign indicates that work is done on the gas, as the gas is expanding against an external pressure.

Summary:
The amount of work done by the expansion of a 0.75 mole of an ideal gas from 15 L to 25 L at 1 atm pressure is -10 atm·L. This negative work value indicates that work is done on the gas during the expansion.