Chemical reaction, a process in which one or more substances, the reactants, are converted to one or more different substances, the products. Substances are either chemical elements or compounds. A chemical reaction rearranges the constituentatoms of the reactants to create different substances as products.
Chemical reactions are an integral part of technology, of culture, and indeed of life itself. Burning fuels, smeltingiron, making glass and pottery, brewing beer, and making wine and cheese are among many examples of activities incorporating chemical reactions that have been known and used for thousands of years. Chemical reactions abound in the geology of Earth, in the atmosphere and oceans, and in a vast array of complicated processes that occur in all living systems.
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 compound, with each molecule composed of two atoms of hydrogen and one atom of oxygen. However, if water, as ice, liquid, or vapour, encounters sodium metal (Na), the 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.
The concept of a chemical reaction dates back about 250 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. In his book Traité élémentaire de chimie (1789; Elementary Treatise on Chemistry), Lavoisier identified 33 “elements”—substances not broken down into simpler entities. 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 Dalton, who postulated his atomic theory early in the 19th century. Dalton maintained that matter is composed of small, indivisible particles, that the particles, or atoms, of 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. Dalton’s theory provided a basis for understanding the results of earlier experimentalists, including the law of conservation of matter (matter is neither created nor destroyed) and the law of constant composition (all samples of a substance have identical elemental compositions).
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.
Chemical Reactions Lab Essay
1131 WordsMar 16th, 20115 Pages
Classifying Chemical Reactions
Purpose: The purpose of this experiment is to observe a variety of chemical reactions and to identify patterns in the conversion of reactants into products.
• Bunsen or lab burner -Test tube clamp
• Butane safety lighter - Test tube rack
• Evaporating dish - Wash bottle
• Forceps or crucible tongs - Wood Splints
• Heat resistant pad
• Litmus paper
• Test tubes
Ammonium carbonate, 0.5g
Calcium carbonate, 0.5g
Copper chloride solution, 4mL
Hydrochloric acid, 4mL
Magnesium ribbon, 2-4 cm strips
Phenolphthalein indicator, 1 drop
Sodium hydroxide solution, 1mL
Sodium phosphate solution, 1mL
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28. Record the observations in the data table.
29. Working in the hood or a designated work area, add about 1 mL of ethyl alcohol to a clean evaporating dish. Place the evaporating dish on a heat- resistant pad.
30. Cap the alcohol bottle and remove it from the work area.
31. Fill a test tube about 1/3 full with cold tap water for use in step 34.
32. Light a butane safety lighter and bring the flame close to the alcohol in the evaporating dish.
33. Turn off the safety lighter as soon as the alcohol ignites.
34. Place the test tube containing cold water in a test tube clamp and hold the test tube above the burning alcohol. Observe the outside of the test tube for evidence of product formation.
35. Allow the alcohol to burn until it is completely consumed.
36. Record observations in the data table.
Observations and Data:
Reaction Appearance of Reactants
1 It got really bright
2 It sizzled, bubbled, and it turned really hot
3 It kept getting smaller and smaller until there was nothing left
4 It sizzled, turned bubbly white, and made crackling noises
5 It broke apart and turned black
6 It looks gunk and blue. It has white stuff at the bottom
7 Turned a dark pink and felt a little cold
8 There was fire and when we put the water over the fire condensation appeared.
Questions and Problems:
1. Write a balanced chemical equation for each reaction #1-8. Classify each reaction using the information provided in the