Anyone help with the percent yield questions?

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.

If two objects at different te,peraure are in contact with each other what happens to their temperature

Areaction is first order with respect to reactant x and second order with respect to reactant y. which statement describes the rate law for this reaction?