An isotope has 2 naturally occurring isotopes. X-107 has an abundance of 51.82% and a mass of 106.9 amu. X-109 has a relative abundance of 48.18% and a mass of 108.9 amu. Calculate the atomic mass. Identify the unknown element.

The enthalpy of formation of water is -285.8 kj/mol. what can be inferred from this statement?

Astudent is trying to create a table that compares hypotheses, theories, and laws. hypothesis theory law do scientific researchers formulate it? yes yes yes does it explain why things happen? yes yes no yes yes yes is it used to make predictions? no yes yes which of the following questions would most likely fill the blank in the table? is it an intelligent guess? is it newly formulated? is it based on observations? has it been proved?

Which statement about hf is true? it is zero for any compound in its standard state. it is positive when the bonds of the product store more energy than those of the reactants. it is negative when a compound forms from elements in their standard states. it is zero for any element that is in the liquid state.