Which of these is indication that a chemical reaction has occurred?

A. Freezing of a substance

B. Melting of a substance

C. Boiling of a substance

D. Formation of a Preciptate

which one of these reactions is energy released? A all reactions B no reactions C endothermic reactions D exothermic reactions

Which two systems are represented in this model? A circulatory and respiratory B. nervous and circulatory C. excretory and respiratory D. nervous and digestive

As you add electrons to an energy level, without adding more protons are there more or less repulsive forces between the electrons?

A reacton has a theoretical yield of 22.8g. When the reaction was carried out, 15.1g of the product was obtained. What is the percent yield?

In which liquid is hydrogen bonding the most significant force of attraction

How are chemical formulas of binary ionic compounds generally written? a cation on left, anion on right b anion on left, cation on right c roman numeral first, then anion, then cation d subscripts first, then ions?

Given a fixed amount of gas held at constant pressure, calculate the volume (in L) it would occupy if a 3.50 L sample were cooled from 90.0oC to 30.0oC.

Which of the following is not required for osmosis to occur? View Available Hint (s) Which of the following is not required for osmosis to occur? selectively permeable membrane water concentration gradient cellular energy

The volume of 1 mole of o2 gas at T=273k P=1atm is? A 6.02 x 10^-23 ml B 760 L C 22.4 L D 2.24 L E 224 L

There are two stable isotopes of bromine. Their masses are 78.9183 and 80.9163 amu. If the average atomic mass of bromine is 79.9091 amu, what is the natural abundance of the heavier isotope? percent abundance of 81Br __%