Reactants are the starting materials in a chemical reaction. Reactants undergo a chemical change in which chemical bonds are broken and new ones formed to make products. Show
In a chemical equation, reactants are listed on the left side of the arrow, while products are on the right side. If a chemical reaction has an arrow that points both left and right, then substances on both sides of the arrow are reactants as well as products (the reaction proceeds in both directions simultaneously). In a balanced chemical equation, the number of atoms of each element is the same for the reactants and products. The term "reactant" first came into use around 1900-1920. The term "reagent" is sometimes used interchangeably A general reaction may be given by the equation: A + B → C In this example, A and B are the reactants and C is the product. There do not have to be multiple reactants in a reaction, however. In a decomposition reaction, such as: C → A + B C is the reactant, while A and B are the products. You can tell the reactants because they are at the tail of the arrow, which points toward the products. H2 (hydrogen gas) and O2 (oxygen gas) are reactants in the reaction that forms liquid water: 2 H2(g) + O2(g) → 2 H2O(l). Notice mass is conserved in this equation. There are four atoms of hydrogen in both the reactant and product side of the equation and two atoms of oxygen. The state of matter (s = solid, l = liquid, g = gas, aq = aqueous) are stated following each chemical formula. In this tutorial, you will learn what a reactant is and where to find a one in a chemical equation. You will also learn the difference between a reactant and a reagent, and be introduced to many examples from relevant chemistry. Topics Covered in Other ArticlesWhat is a Reactant?The term reactant is used to help describe a chemical equation. A reactant is a chemical substance that is present at the start of a chemical reaction, and is changed as the chemical reaction proceeds. They could also be referred to as terms like starting materials or reagents. You could also describe a reactant, as something that is present at the beginning of a chemical reaction, and then partially or completely consumed to make the products. Reactants are found to the left of a chemical equation, before the arrow. For example, in the first equation A and B are reactants and for the second AB and CD are the reactants. A + B → C AB + CD → AD + CB This rule applies to these above examples, but also to a vast assortment of other types of reactions. As another example, plants use carbon dioxide and water to make glucose, which is essential to making energy for life. CO2 + H2O → C6H12O6 + O2 The materials the plant is using (and changing) are CO2 and H2O. These are our reactants. Equilibrium Arrows: Where are the reactants?In reactions that can proceed both backwards and forwards, equilibrium arrows are used to show that the chemistry can run in both directions. In this case, reactants are found on both the left and the right of the chemical equation. 2. A + B → C 3. C → A + B Equation 1 is telling us that equation 2 and 3 are both able to occur. In equation 1, A and B, but also C are reactants. Reactants vs. ReagentsReactants are consumed when a chemical reaction takes place, and a reagent does not have to be consumed. An example of a reagent is a catalyst, which is a material that helps to speed up the reaction, but is unchanged throughout the process. Catalysts can be small molecules, or large complex structures such as enzymes. In organic chemistry, there are many commonly used reagents, an example is an organometallic reagent like Me-MgBr (pictured below). This is called a Grignard reagent. Since Me-MgBr it is altered in the reaction, it is also considered a reactant. Grignard reagent Me-Mg-Br combined with a second reactant, Me-Cl, forms a new molecule.Note: Solvents, although present when many reactions take place, are not considered reactants or reagents. Further ReadingAre you loving this? Not loving this? Please consider taking a moment to share your feedback with us. Thanks!
The teacher will use a small candle flame to demonstrate a chemical reaction between the candle wax and oxygen in the air. Students will see a molecular animation of the combustion of methane and oxygen as a model of a similar reaction. Students will use atom model cut-outs to model the reaction and see that all the atoms in the reactants show up in the products. ObjectiveStudents will be able to explain that for a chemical reaction to take place, the bonds between atoms in the reactants are broken, the atoms rearrange, and new bonds between the atoms are formed to make the products. Students will also be able to explain that in a chemical reaction, no atoms are created or destroyed. EvaluationDownload the student activity sheet, and distribute one per student when specified in the activity. The activity sheet will serve as the “Evaluate” component of each 5-E lesson plan. SafetyBe sure you and the students wear properly fitting goggles. Be careful when lighting the candle. Be sure that the match and candle are completely extinguished when you are finished with the demonstration. Materials for the Demonstration
Materials for Each Student
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