4. Read these sentences from the article. "Individual layers of ancient sediment form horizontal stripes on the rock. From a few
steps back, the rock wall looks like a cross-section of a giant, stone encyclopedia."
Why might the author have included this description of the rock wall?
A. to explain why the author quotes scientists in the article
B. to demonstrate why the author explains two different methods used to date the rise of
oxygen in the atmosphere
C. to show why the author presents information about different compounds in the article
D. to clarify why the author compares studying a rock formation to studying a book

These questions are based on the attached photo. the experiment is about burning magnesium metal with oxygen. 1. write the balanced chemical equation for the reaction you are performing. 2. calculate the mass of magnesium metal used in each trial. o trial 1: o trial 2: 3. calculate the actual yield of magnesium oxide for each trial. o trial 1: o trial 2: 4. magnesium is the limiting reactant in this experiment. calculate the theoretical yield of mgo for each trial. o trial 1: o trial 2: 5. determine the percent yield of mgo for your experiment for each trial. o trial 1: o trial 2: 6. determine the average percent yield of mgo for the two trials. your company currently uses a process with a similar cost of materials that has an average percent yield of 91 percent. if the average percent yield of this process is higher than that, this could save the company money. what is your recommendation to the company? support your recommendation using your data, calculations, and understanding of stoichiometry gathered from this lab.

13. a covalent bond between two atoms is likely to be polar if: a. one of the atoms is much more electronegative than the other. b. the two atoms are equally electronegative. c. the two atoms are of the same element. d. the bond is part of a tetrahedrally shaped molecule. e. one atom is an anion.

What is the value of the standard enthalpy of formation of an element in its most stable form?