Modeling Chemical Reactions

Modeling Chemical Reactions

Topic 2, Lesson 3

Chemical Equations

• Chemical Equations are used for comminutes information to summarize a chemical reaction.

• Chemical equations convey or express 3 things: Identities of the molecules involved in the reaction, the elements that make up those molecules, and whether the molecules are products or reactants.

Formulas

• chemical formulas combine the symbols of different elements to represent molecules.

• H₂0 H is the symbol for Hydrogen, O is the symbol for Oxygen on the periodic table

• subscript (little number next to the symbol) shows how many atoms of that element are in the molecule

• No subscript means only one atom of that element

• for H₂O there are 2 atoms of Hydrogen, 1 atom of Oxygen

Structure of an Equation

• The formulas for the reactants are written on the Left of the arrow

• the arrow means "yields" or "reacts to form"

• The formulas for the products are written to the right of the arrow

• if there are two or more reactants, they are separated by a + sign. If two or more products are formed, they are also separated by a + sign

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Coefficients

• the numbers on the front of each component in the equation show how many particles of the reactant are needed and how many particles of the products are formed during the reaction.

• Coefficients help balance the equation so that the number of atoms in the reactants equals the number of the atoms in the products.

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Chemical Reactions and Equations

• the number of reactants and products can vary

• some reactions have only one reactant or product.

• other reactions have two, three, or more reactants or products

Law of Conservation of Mass

• during a chemical reaction, matter is neither created or destroyed.

• all atoms that are present at the beginning of a chemical reaction are present at the end of the reaction.

• even though products may have different properties from the reactants, the total mass does not change.

• This is the reason for coefficients are used for balancing equations.

Open Systems

• If matter can enter and escape from a system, it may appear that matter is lost or gained adn in violation of the principle of conservation of mass., but this is not the case.

• example: photosynthesis-carbon dioxide flows and very difficult to follow how much etc.

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Closed systems

• better place to measure the movement of matter and study reactions that involve gas.

• scientists sometimes use closed system (plants in a sealed container) to study gases etc.

3 General Types of Chemical Reactions

• Synthesis

• Decomposition

• Replacement

Synthesis Reactions

• synthesize means to "put things together"

• when two or more elements come together to form a more complex substance

• 2Mg + 0_{2 —‣ 2MgO}

Decomposition

• opposite of Synthesis Reaction

• compounds break down into simpler products

• 2H₂O₂ —> 2H₂O + O₂

• you can see where a more complex compound was broken down to 2 simpler

Replacement reaction

• when one element replaces another element in a compound, or if two elements in different compounds trade places.

• the chemical equation looks likes elements did a switcheroo.

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Multiple Choice

The reactant and products involved in a chemical reaction are shown in the chemical equation.

• True

• False

Multiple Choice

The Law of Conservation of Mass states that matter is neither created nor _________________ .

• rearranged

• remade

• destroyed

Multiple Choice

A chemical equation summarizes a chemical reaction.

• True

• False

Multiple Select

If there is no ___________ in a chemical equation, it means there is only one atom of that element.

• subscript

• coefficient

• symbol

Multiple Choice

All of the atoms present at the beginning of a chemical reaction are present at the end of a chemical equation.

• True

• False

Multiple Choice

In an open system, matter cannot enter or escape, therefore making it easy to measure the movement of matter and study reactions.

• True

• False

Multiple Choice

Reaction in which two or more elements combine to form more complex substance

• synthesis reaction

• decomposition reaction

• replacement reaction