Why is matter conserved in a chemical reaction

Natural product chemists, who design and execute syntheses of complex biological molecules, will typically start a synthesis with KILOS of starting material. How matter is conserved during chemical reactions? Andrea B. May 14, Explanation: All the atoms you had at first, are conserved in the new state also if arranged in a different way. This concept is called the Law of Conservation of Mass. Water, for example, is made up of two hydrogen atoms and one oxygen atom. Water is the only known substance on Earth that exists naturally in three states: solid, liquid, and gas.

To change between these states, water must undergo physical changes. When water freezes, it becomes hard and less dense, but it is still chemically the same. To form water, however, hydrogen and oxygen atoms must undergo chemical changes.

The addition or subtraction of atomic bonds changes the chemical properties of the substances involved. Both hydrogen and oxygen are diatomic —they exist naturally as bonded pairs H 2 and O 2 , respectively. In the right conditions, and with enough energy, these diatomic bonds will break and the atoms will join to form H 2 O water.

Chemists write out this chemical reaction as:. This equation says that it takes two molecules of hydrogen and one molecule of oxygen to form two molecules of water.

Notice that there are the same number of hydrogen atoms and oxygen atoms on either side of the equation. In chemical changes, just as in physical changes, matter is conserved. The difference in this case is that the substances before and after the change have different physical and chemical properties.

Hydrogen and oxygen are gases at standard temperature and pressure, whereas water is a colorless, odorless liquid. Ecosystems have many chemical and physical changes happening all at once, and matter is conserved in each and every one—no exceptions. Consider a stream flowing through a canyon—how many chemical and physical changes are happening at any given moment? For many canyon streams, the water comes from higher elevations and originates as snow.

But in the context of the canyon stream, it began in the mountains as snow. The snow must undergo a physical change —melting—to join the stream. As the liquid water flows through the canyon, it may evaporate another physical change into water vapor. Water gives a very clear example of how matter cycles through our world, frequently changing form but never disappearing.

Next, consider the plants and algae living in and along the stream. In a process called photosynthesis , these organisms convert light energy from the sun into chemical energy stored in sugars.

Rather, the extra mass is held in the system as a whole. Depending on the position and state of particles in a system relative to each other, the system gains or loses mass in addition to the individual masses of the particles. This concept is very similar to the classical concept of potential energy, but we now know that the energy is actually stored as mass.

If you measure with very sensitive equipment the sum of the mass of two million hydrogen atoms and one million oxygen atoms that are separated from each other, then measure the mass of one million water molecules, you will find theses masses to be different.

Topics: chemical reaction , conservation of energy , conservation of mass , energy , mass , reaction. Every chemical reaction involves conversion between energy and mass. Public Domain Image, source: Christopher S. If a liquid evaporates inside a sealed container then they believe that the combined weight of the container and the liquid will be reduced by the weight of the liquid because it has apparently disappeared.

Although at this level the majority of students will have an understanding of the particle nature of atoms, for many the numbers of atoms are not conserved during chemical reactions. For example, the number of atoms appears to grow in the bark of trees, and their numbers drop during processes such as combustion or decay and increase during photosynthesis.

The idea of indivisible atoms helps to explain the conservation of matter. If the number of atoms stays the same no matter how they are rearranged, then their total weight stays the same. In all physical and chemical changes, the total number of atoms remains the same, hence when substances interact with one another, combine or break apart, the total weight of the system remains the same.

Growing plants obtain their new carbon the great majority of their dried weight from carbon dioxide i. When we lose weight by dieting or exercise, most of the loss is from breathing out the carbon atoms metabolised from our fat as carbon dioxide. When a liquid evaporates in a sealed container, the weight stays the same; the gas particles are affected by gravity in the same way as tennis balls and they consequently hit the bottom surface of the container with more force than they hit the top.

In your teaching of conservation of matter and hence weight, students need to be encouraged to change their views from those based on their everyday experiences to more scientific views such as the idea that there are only a fixed number of particles in the world and these building blocks are continually being rearranged into new things. This is a difficult, abstract idea and we can use analogies to assist students with understanding. One of the difficulties is that closed systems involving changes such as combustion and respiration are almost impossible to set up and weigh in a classroom.

You can disprove by experiment only a few of the common alternative conceptions in this area. It is important to discuss a variety of change situations that appear to involve non-conservation of matter and to revisit this issue in other topics such as ecosystems, food and diet, and sources of energy.

Students should be encouraged to make predictions about these processes in a supportive classroom environment where they can be assisted to develop new theories, critically analyse their understandings and those of others, and compare these with scientific views presented by the teacher.