Ch.1 - Intro to General ChemistryWorksheetSee all chapters
All Chapters
Ch.1 - Intro to General Chemistry
Ch.2 - Atoms & Elements
Ch.3 - Chemical Reactions
BONUS: Lab Techniques and Procedures
BONUS: Mathematical Operations and Functions
Ch.4 - Chemical Quantities & Aqueous Reactions
Ch.5 - Gases
Ch.6 - Thermochemistry
Ch.7 - Quantum Mechanics
Ch.8 - Periodic Properties of the Elements
Ch.9 - Bonding & Molecular Structure
Ch.10 - Molecular Shapes & Valence Bond Theory
Ch.11 - Liquids, Solids & Intermolecular Forces
Ch.12 - Solutions
Ch.13 - Chemical Kinetics
Ch.14 - Chemical Equilibrium
Ch.15 - Acid and Base Equilibrium
Ch.16 - Aqueous Equilibrium
Ch. 17 - Chemical Thermodynamics
Ch.18 - Electrochemistry
Ch.19 - Nuclear Chemistry
Ch.20 - Organic Chemistry
Ch.22 - Chemistry of the Nonmetals
Ch.23 - Transition Metals and Coordination Compounds

A physical change involves a change in the phases of matter, whereas a chemical change involves a change in chemical bonds. 

Understanding Mixtures

Concept #1: Homogeneous vs. Heterogeneous Mixtures


Last time we met, we said that Chemistry is the study of matter. Matter is anything that has mass and takes up space. Basically matter is everything around us: tables, the books that we're reading, TV, our cars, even ourselves. Everything is matter.
Now, we're going to say that most matter consists of basically mixing different things together. We're going to mix pure substances together, different elements mixed together to give us these mixtures. We're going to say that these mixtures can be broken down into two categories. We're going to say blank mixtures have no indistinguishable parts.
This first type of mixture basically means when I mixed them together, I can't tell which part is which. A good example here is if we have red bull and vodka. When we mixed these two things together, they give us this pale yellow solution here. I can't tell which part is red bull, I can't tell which part is vodka. All I know is that it taste okay, that's all I really know.
We're going to say that this type of mixture is known as a homogenous mixture. I can't tell the different parts from one another. Everything mixes well together. We're going to say homogenous mixture mixed together uniformly. We're going to say it’s a uniform mixture. All the parts mixed perfectly together.
The next type of mixture does have distinguishable parts. We've all heard this before, oil and water don't mix. That's because they form a heterogeneous mixture. I can tell just from looking which part is water, which part is oil. This is basically a non-uniform mixture. 

Physical & Chemical Changes

Concept #2: Physical vs. Chemical Changes


We also talked about Chemistry not only being the study of matter, but the changes that matter undergoes. We're going to say that this is broken down into two types of category. We're going to have our physical changes and our chemical changes.
Now, in the first blank, we have their changes in the form of the substance, but not its chemical composition. Basically, we're going to say that these are physical changes. What do I mean by not a change in its chemical composition? For example, I have ice—which is solid water and then I just leave it out and it melts. It goes from solid water to liquid water.
At the end of the reaction, it's still water. It began as water. It's still water at the end. I didn't change its chemical makeup. Once I change its chemical makeup or chemical composition, it should stop being water. It should change into something entirely different.
Now the second type of change creates new substances with different properties and different chemical compositions, so we say that this is chemical. For example, I have that liquid water and I super heat it. That little triangle means heat, so I super heat the water, that ice, heat it so much so, then now it becomes H2 gas and O2 gas. It becomes hydrogen gas and oxygen gas.
It started off as water, but now it's no longer water. It's hydrogen gas and oxygen gas which are very different from water. As a result, because they're so different from water, they're going to have different properties, different melting points, different boiling points, different densities. That's what we mean by a chemical change. 

In a physical change there is a change in matter as it goes from one physical state to another. In a chemical change atoms rearrange themselves to create a new substance. 

Example #1: Which of the following represents a physical change? 

a.  Alkanes burn spontaneously.

b.  The sublimation of CO2.

c.  2 H2 (g) +  O2 (g) ----> 2 H2O (g)

d.  The rusting of a car.