问题
单项选择题
精馏的原理是根据混合物的()不同,相对挥发度不同,在一定条件下,混合物各组分都在汽液相间建立各自的平衡关系,不平衡的汽液两相经过热交换,汽相多次部分冷凝,液相多次部分汽化达到分离的过程。
A.泡点
B.沸点
C.露点
答案
参考答案:B
精馏的原理是根据混合物的()不同,相对挥发度不同,在一定条件下,混合物各组分都在汽液相间建立各自的平衡关系,不平衡的汽液两相经过热交换,汽相多次部分冷凝,液相多次部分汽化达到分离的过程。
A.泡点
B.沸点
C.露点
参考答案:B
As viewed from space, the Earth’s distinguishing characteristics are its blue waters and white clouds. Enveloped by an ocean of air consisting of 78% nitrogen and 21% oxygen, the planet is the only one in our solar system known to harbor life. Circling the Sun at an average distance of 149 million km (93 million miles), the Earth is the third planet from the Sun and the fifth largest planet in the solar system. Its rapid and molten nickel-iron core give rise to an extensive magnetic field which, coupled with the atmosphere, shields us from nearly all of the harmful radiation coming from the Sun and other stars. Most meteors burn up in the Earth’s atmosphere before they can strike the surface. The planet’s active geological processes have left no evidence of the ancient pelting it almost certainly received soon after it was formed. The Earth has a single natural satellite-the Moon. |
Approximately how much of the Earth’s atmosphere is nitrogen
A.One-fourth
B.One-half
C.Three-fourths
D.All of it