ANSWER Since 1.0 × 10 -7 has two significant figures, the pH can be reported as 7.00. A logarithmic scale condenses the range of acidity to numbers that are easy to use. Consider a solution with [H + ] = 1.0 × 10 -4 M. That is a hydrogen-ion concentration that is 1000 times higher than the concentration in pure water.
Since the question says “these” I assume it was multiple choice...but anyways, intermolecular forces between some of the water molecules are breaking apart. The H2O is going from a tightly packed solid of a fixed volume to a liquid with molecules moving faster and less bonds, which can take the shape of its container. It requires energy to break a bond, so this is an endothermic process.
