When Nitrogen gas gets cold enough it can form a liquid. This liquid nitrogen is an example of what?
A. A chemical change because it took a significant temperature drop to convert
nitrogen from gas to liquid.
B. A chemical change because the nitrogen underwent a conversion from gas to a
liquids.
C. A physical change because it was only a state change from solid to liquid.
D. A physical change because the temperature drop causes the molecules to completely rearrange.

the answers would be

the first one and the second one

one negative thing it that it can kill water animals. another negative thing is it can cause the destruction of ecosystem. one way water pollution can be reduced is to conserve energy.

answer: semi-infinite solid initially at a uniform temperature of 400 ◦c is cooled at its surface by convection. the cooling fluid at a constant temperature of 200 ◦c has a convective coefficient (ha) of 250 w/m2.k. the physical properties of the solid: k = 20 w/m.k and α = 4 * 10-5  m2/s. using δx = 0.04 m and δt = 10 s. write the finite difference equations describing the transient heat transfer of the first five δx and the temperature profile after 30 s.

the population of unionid mussels in the hudson river decreased after zebra mussels were introduced. zebra mussels, a nonnative species, competed with the unionid mussels for food. the zebra mussels were able to outcompete the unionid mussels, allowing the zebra mussel population to increase dramatically over six years. the unionid mussel population decreased due to a lack of food.

hope this :