UNIT 3: CONSERVATION OF MASS & ENERGY IN CHEMICAL REACTIONS

Vocabulary flashcards covering key concepts from the 'Conservation of Mass & Energy in Chemical Reactions' lecture unit.

Law of Conservation of Mass

Matter is neither created nor destroyed during chemical reactions; the number and types of atoms in reactants equal those in products.

Reactants

The starting substances in a chemical reaction, typically found on the left side of a chemical equation.

Products

The substances formed as a result of a chemical reaction, typically found on the right side of a chemical equation.

Balanced Chemical Equation

A chemical equation where the number of atoms of each element is equal on both the reactant and product sides.

Chemical Bonds

The forces that hold atoms together, which are broken and formed during chemical reactions as atoms rearrange.

Endothermic Reaction

A chemical reaction that absorbs energy from its surroundings, often indicated by a decrease in temperature.

Exothermic Reaction

A chemical reaction that releases energy into its surroundings, often indicated by an increase in temperature.

Coefficient

A number placed in front of a chemical formula in a balanced equation, indicating the number of molecules or moles of that substance.

Subscript

A number written below and to the right of a chemical symbol in a formula, indicating the number of atoms of that element in a molecule.

Closed System

An experimental setup designed to prevent matter from entering or leaving, crucial for accurately studying the conservation of mass in reactions.

Energy Transfer

The movement or conversion of energy during a chemical reaction, either absorbed from or released into the surroundings.

Computational Thinking (Chemistry)

The ability to analyze chemical equations by calculating the number of atoms to confirm that all atoms in reactants appear in products, supporting the Law of Conservation of Mass.

What does the Law of Conservation of Mass state?

Matter is neither created nor destroyed in a chemical reaction.  The number of atoms in the reactants equals the number in the products.  EXAMPLE: in a sealed container, the mass before and after a reaction stays the same.

In a chemical equation, how can you identify the reactants and products?

Reactants are on the LEFT side of the arrow (the starting substances).  Products are on the RIGHT side of the arrow (the new substances formed). 

Why must chemical equations be balanced? What does a coefficient represent? What does a subscript represent?

• Equations must be balanced to follow the Law of Conservation of Mass (same number of atoms on both sides).

• Coefficient = big number in front; shows how many molecules are present.

• Subscript = small number after an element; shows how many atoms of that element are in one molecule.

When atoms rearrange during a chemical reaction, what happens to the bonds between atoms?

• Old bonds break, and new bonds form, creating new substances.

. What is the difference between an endothermic and an exothermic reaction? How can temperature data help you identify these reactions?

• Endothermic: absorbs energy (temperature goes down). Example: ice melting, photosynthesis.

• Exothermic: releases energy (temperature goes up). Example: burning wood, fireworks.

• Temperature data shows if heat is absorbed (cooler) or released (warmer).

Why is it important to conduct chemical reaction experiments in closed systems when studying conservation of mass?

• To prevent gases or substances from escaping.

• This ensures the mass before = mass after, proving conservation of mass.

Given a chemical equation, count the number of atoms of each element in the reactants and products. Example: 2H₂ + O₂ → 2H₂O

• Reactants: 4 H, 2 O

• Products: 4 H, 2 O

• Balanced = atoms conserved.

Describe an experiment to prove that mass is conserved during a chemical reaction.

• Place vinegar and baking soda in a sealed container. Measure the mass before and after the reaction.

• Even though gas (CO₂) forms, the total mass stays the same if nothing escapes.

How do chemical bonds break and form during a reaction?

• Energy is used to break old bonds.

• New bonds form, releasing or absorbing energy.

In a chemical reaction, the total mass of the reactants is

Exactly equal to the total mass of the products.