Copper is added to a solution of nitric acid. the solution becomes hot and changes from colorless to dark blue. what is the best explanation for the change in temperature?
a.
the copper and nitric acid repel each other, which produces heat.
b.
the increased volume of the solution causes heat to be released.
c.
the chemical reaction between the copper and the nitric acid produces heat.
d.
the blue color absorbs less energy, which causes heat to be released.

Agroup of students is studying convection current. they fill two identical balloons with the same amount of helium. one balloon is placed in a freezer and the other is in an area with warm air. after 10 minutes, the balloon are released from a height of 1 meter. which of the following to the students most likely observe? a) the warm balloon expands and rises. the cold balloon shrinks and sinks b) the balloon both rise. the cold balloon is larger than the warm balloon c) the cold balloon expands and rises. the warm balloon shrinks and sinks d) the balloon rise at the same rate. both balloons are the same size