理想气体是理论上假想的一种把实际气体性质加以简化的气体。人们把假想的，在任何情况下都严格遵守气体三定律的气体称为理想气体。就是说：一切实际气体并不严格遵循这些定律，只有在温度较高，压强不大时，偏离才不显著。所以一般可认为温度不低于0℃，压强不高于1.01×105Pa时的气体为理想气体。An ideal gas is a theoretical hypothetical gas which simplifies the properties of an actual gas. A hypothetical gas that strictly obeys the three laws of gas in all circumstances is called an ideal gas. That is to say, all real gases do not strictly follow these laws, and only at high temperatures and low pressures does the deviation become insignificant. Therefore, it can be generally regarded as an ideal gas when the temperature is not lower than 0℃ and the pressure is not higher than 1.01×105Pa.