Reaction Time

1. Reaction Time By: Cole Johnson and Jessica Andrews

2. What is a Chemical Reaction? • A Chemical Reaction occurs when one or more reactants change into one or more products.

3. Why do reactions take place? • Take making bread for example, the Chemical Reaction takes place when the ingredients are mixed together and heated in the oven.

4. Just what is a Chemical Equation? • A chemical equation is a representation of a chemical reaction; the formula of the reactants (on the left) are connected by an arrow with the formulas of the products (on the right). • We use a chemical equation because it’s a quick, shorthand notation—to convey as much information as possible about what happens in a chemical equation.

5. Should they be balanced? • Yes, because if you start with a certain quantity of something, you must end with the same quantity. Matter cannot be created or destroyed.Think of a chemical reaction like building Lego structures. You have a car made with 100 Lego blocks, you take it apart and you put it back together to make a 100-block boat. Chemical reactions are merely re-distributions of the atoms to make new compounds.

6. What is the difference between Reactants and Products? • a reactant is what you start with and the product is what you end up with. For example, if you have two hydrogen and one oxygen (reactants) you put them together and you get H2O (product).

7. What does the arrow mean in a chemical equation? • The arrow separates the reactant from the product. You read the arrow as yields, gives, or reacts to produce.

8. What is a precipitate? • A precipitate is a solid that forms and settles out of a liquid mixture • When you’re mixing solutions of two ionic compounds can sometimes result in the formation of an insoluble salt called precipitate. • You can predict the formation of a precipitate by using the general rules for solubility of ionic compounds.

9. How do you balance a chemical Reaction? • Apply the Law of Conservation of Mass to get the same number of atoms of every element on each side of the equation. Tip: Start by balancing an element that appears in only one reactant and product. • Once one element is balanced, proceed to balance another, and another, until all elements are balanced. • Balance chemical formulas by placing coefficients in front of them. Do not add subscripts, because this will change the formulas.

10. Synthesis Reaction-a chemical change in which two or more substances react to form a single new substance. When two nonmetals react in a combination reaction, more than one product is often possible. A+B --> AB Ex: 2K + I2 --> 2KI Annie meets Bob and do the deed. Decomposition Reaction- a chemical change in which single compound breaks down into two or more simpler products. It involves only one reactant and two or more products. AX ---- A + X Ex:2HgO-- 2Hg(l) +O2(g) When a corpse decomposes it breaks down Synthesis and Decomposition Reactions

11. Single Displacement- a chemical change which one element replaces a second element in a compound You can Identify a single-replacement reaction by noting that both the reactants and the products consist of an element and a compound A + BC = AB + C Zn + 2HCl ---> ZnCl2 + H2 B and C were dating and A took B away from C = ( Double Displacement- a chemical change involving an exchange of positive ions between two compounds Also known as double displacement reactions, and generally takes place in aqueous solution and often produce a precipitate, a gas, or a molecular compound such as water. AB + CD = AC + BD Ex:AgNO3 + HCl AgCl + HNO3 AB and CD are out on a date when A and C decide to switch dates. Single and Double Displacement

12. Combustion Reaction • A chemical change in which an element or a compound reacts with oxygen, often producing energy in the form of heat and light. • It always involves oxygen as a reactant • CxHy + O2 --> CO2 + H2O • Ex:CH4[g] + 2 O2[g] -> CO2[g] + 2 H2O[g] + energy  • (hint: spontaneous combustions or car explosions)