Template:HideTOC 2.1: What is Matter? Matter is anything that has mass and volume (takes up space). For most common objects that we deal with every day, it is fairly simple to demonstrate that they have mass and take up space. You might be able to imagine, however, the difficulty for people several hundred years ago to demonstrate that air has mass and volume. Air (and all other gases) are invisible to the eye, have very small masses compared to equal amounts of solids and liquids, and are quite easy to compress (change volume). 2.2: Classifying Matter According to Its State—Solid, Liquid, and Gas Three states of matter exist - solid, liquid, and gas. Solids have a definite shape and volume. Liquids have a definite volume, but take the shape of the container. Gases have no definite shape or volume 2.3: Classifying Matter According to Its Composition One useful way of organizing our understanding of matter is to think of a hierarchy that extends down from the most general and complex to the simplest and most fundamental. Matter can be classified into two broad categories: pure substances and mixtures. A pure substance is a form of matter that has a constant composition and properties that are constant throughout the sample. A material composed of two or more substances is a mixture. 2.4: Differences in Matter- Physical and Chemical Properties A physical property is a characteristic of a substance that can be observed or measured without changing the identity of the substance. Physical properties include color, density, hardness, and melting and boiling points. A chemical property describes the ability of a substance to undergo a specific chemical change. 2.5: Changes in Matter - Physical and Chemical Changes Change is happening all around us all of the time. Just as chemists have classified elements and compounds, they have also classified types of changes. Changes are either classified as physical or chemical changes. Chemists learn a lot about the nature of matter by studying the changes that matter can undergo. Chemists make a distinction between two different types of changes that they study - physical changes and chemical changes. 2.6: Conservation of Mass - There is No New Matter The law of conservation of mass states that matter can not be created or destroyed in a chemical reaction. So the mass of the product equals the mass of the reactant. A reactant is when two or more elements chemically interact to make a new substance and a product is the substance that is formed as the result of a chemical reaction. Mass and matter may not be able to be created or destroyed, but it can change forms to other substances like liquids, gasses, solids, etc. 2.7: Energy and Chemical and Physical Change Phase changes involve changes in energy. All chemical reactions involve changes in energy. This may be a change in heat, electricity, light, or other forms of energy. Reactions that absorb energy are endothermic. Reactions that release energy are exothermic. 2.8: Temperature - Random Motion of Molecules and Atoms Three different scales are commonly used to measure temperature: Fahrenheit (expressed as °F), Celsius (°C), and Kelvin (K). 2.9: Temperature Changes - Heat Capacity The specific heat of a substance is the amount of energy required to raise the temperature of 1 gram of the substance by 1 degree Celsius. 2.10: Energy and Heat Capacity Calculations Heat is a familiar manifestation of transferring energy. When we touch a hot object, energy flows from the hot object into our fingers, and we perceive that incoming energy as the object being “hot.” Conversely, when we hold an ice cube in our palms, energy flows from our hand into the ice cube, and we perceive that loss of energy as “cold.” In both cases, the temperature of the object is different from the temperature of our hand. Template:HideTOC