Answer: V₂ = 37.71mL
Step-by-step explanation: To determine the new volume of Helium gas, use the Combined Gas Law, which states the following relationship among pressure, volume and temperature:
![(P_(1)V_(1))/(T_(1)) =(P_(2)V_(2))/(T_(2))](https://img.qammunity.org/2022/formulas/chemistry/high-school/jfduiqu6zah1zqyljubf4jrc1mul266xa7.png)
where index 1 relates to the initial state of the gas and index 2 to the final state of the gas.
Temperature is in Kelvin, so:
T = °C + 273
For this situation, standard pressure is 1 atm. Temperatures will be:
T₁ = 20 + 273 = 293 K
T₂ = 91 + 273 = 364 K
Solving:
![V_(2)=(T_(2)P_(1)V_(1))/(P_(2)T_(1))](https://img.qammunity.org/2022/formulas/chemistry/high-school/htnwsvzy5cxkbc734p9f65mav6af894vvt.png)
![V_(2)=(364*1*85)/(2.8*293)](https://img.qammunity.org/2022/formulas/chemistry/high-school/yj07bsik7xhsqlu94gbc9r5fjzlolu2z52.png)
![V_(2)=(30940)/(820.4)](https://img.qammunity.org/2022/formulas/chemistry/high-school/3gnn21680cdq5c8vhgxrppxtbj3w5d63dp.png)
37.71
The new volume of He gas is 37.71 mL.