Reactions occur when two or more molecules interact and the molecules change. Bonds between atoms are broken and created to form new molecules. What molecules are they? How do they interact?
In many cases the properties of a mixture are determined primarily by forces that are more properly classified as chemical rather than as physical.
For example, when dinitrogen pentoxide is dissolved in water, a new substance, nitric acid, is formed; and it is… Chemical reactions must be distinguished from physical changes.
Physical changes include changes of state, such as ice melting to water and water evaporating to vapour. If a physical change occurs, the physical properties of a substance will change, but its chemical identity will remain the same.
No matter what its physical state, water H2O is the same compoundwith each molecule composed of two atoms of hydrogen and one atom of oxygen. However, if water, as ice, liquidor vapour, encounters sodium metal Nathe atoms will be redistributed to give the new substances molecular hydrogen H2 and sodium hydroxide NaOH.
By this, we know that a chemical change or reaction has occurred. Historical overview The concept of a chemical reaction dates back about years.
It had its origins in early experiments that classified substances as elements and compounds and in theories that explained these processes. Development of the concept of a chemical reaction had a primary role in defining the science of chemistry as it is known today.
The first substantive studies in this area were on gases. The identification of oxygen in the 18th century by Swedish chemist Carl Wilhelm Scheele and English clergyman Joseph Priestley had particular significance.
The influence of French chemist Antoine-Laurent Lavoisier was especially notable, in that his insights confirmed the importance of quantitative measurements of chemical processes. Among his many discoveries, Lavoisier accurately measured the weight gained when elements were oxidized, and he ascribed the result to the combining of the element with oxygen.
The concept of chemical reactions involving the combination of elements clearly emerged from his writing, and his approach led others to pursue experimental chemistry as a quantitative science.
The other occurrence of historical significance concerning chemical reactions was the development of atomic theory. For this, much credit goes to English chemist John Daltonwho postulated his atomic theory early in the 19th century.
Dalton maintained that matter is composed of small, indivisible particles, that the particles, or atomsof each element were unique, and that chemical reactions were involved in rearranging atoms to form new substances.
This view of chemical reactions accurately defines the current subject. Thus, experiment and theory, the two cornerstones of chemical science in the modern world, together defined the concept of chemical reactions.
Today experimental chemistry provides innumerable examples, and theoretical chemistry allows an understanding of their meaning. Basic concepts of chemical reactions Synthesis When making a new substance from other substances, chemists say either that they carry out a synthesis or that they synthesize the new material.
Reactants are converted to products, and the process is symbolized by a chemical equation. For example, iron Fe and sulfur S combine to form iron sulfide FeS. The state of matter of reactants and products is designated with the symbols s for solidsl for liquidsand g for gases.
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Kinetic energy is determined by the movement of an object -- or the composite motion of the components of an object - and potential energy reflects the potential of an object to have motion, and generally is a function of the position of an object.