Final answer:
The U.L.C. rating on a fire extinguisher describes its effectiveness against different types of fires. For a 10A 20BC extinguisher, it means it's suitable for ordinary combustibles and flammable liquids and is safe for electrical fires. When applied to a CO2 extinguisher heated in a car, the ideal gas law can determine the change in internal pressure due to temperature increase.
Step-by-step explanation:
The U.L.C. (Underwriters Laboratories of Canada) rating on a multipurpose fire extinguisher indicates the types and sizes of fires that the extinguisher is capable of putting out. In the case of a 10A 20BC rated fire extinguisher, '10A' signifies that it is equivalent to 10 gallons of water and effective against ordinary combustibles like wood and paper, while '20BC' means it can handle 20 square feet of a Class B fire (flammable liquids) and is also effective against Class C fires (electrical fires).
For the question related to a CO₂ fire extinguisher left inside a car, we can apply the ideal gas law to find the internal pressure when the temperature rises. The ideal gas law is PV = nRT, where P is pressure, V is volume, n is the number of moles of gas, R is the ideal gas constant, and T is temperature. As the volume and the amount of gas do not change, the relationship between pressure and temperature is direct, provided that the temperatures are in absolute units (Kelvins).
Converting the initial and final temperatures to Kelvins, and using the initial condition provided (20.0 atm at 21°C), we can calculate the final pressure after the temperature in the car reaches 71.1°C by setting up a proportion given the initial pressure and temperature conditions. This assumes that the fire extinguisher conforms to the ideal gas behavior, which is a common assumption for gases at non-extreme conditions.