What is an exothermic reaction? a. a reaction that is cold
b. a reaction that describes the forming of bonds
c. a reaction that requires heat
d. a reaction that takes in energy from outside itself

Nuclear fusion is the source of energy for stars. besides hydrogen, which other element is most likely also common in stars?

Blank allows you to do calculations for situations in which only the amount of gas is constant a)boyle's law b)combined gas law c)ideal gas law d)dalton's law

Which of the following is an example of physical change not a chemical change? a) a log gives off heat and light as it burns. b) a tree stores energy from the sun in its fruit. c) a penny lost in the grass slowly changes color. d) a water pipe freezes and cracks on a cold night.