Chemistry/Physical Setting The Nature of Gases Br. Jabreal

Aim: What is the nature of gases? Do Now: Describe the arrangement of particles in a gas, and draw a phase diagram for a gas made up of the following substance:

Kinetic Theory and a Model for Gases Kinetic energy: Energy of an object resulting from its motion. Kinetic Theory: All matter consists of tiny particles in constant motion. Particles of gases are usually molecules or atoms. The kinetic theory is used to explain the behavior of gases and contains a few assumptions.

Kinetic Theory Applied to Gas includes following assumptions: 1. Particles in a gas considered to be small, hard spheres with an insignificant volume Particles spaced out very much and exert no attractive or repulsive forces on each other. 2. The motion of the particles in a gas is rapid, constant, and random This explains why gases fill the space of containers the are in regardless of the size or shape of the container. 3. All collisions between particles are perfectly elastic During elastic collisions, kinetic energy completely transferred between particles without any being lost

Gas Pressure Gas pressure is the force exerted by a gas per unit surface area of an object. This force is caused by the collision of billions of rapidly moving gas particles colliding with an object When a balloon is filled with air, why does it maintain a shape? Because of the pressure from air particles colliding with the inside of the balloon. If no particles present, no pressure and called Vacuum.

Atmospheric Pressure Atmospheric Pressure: The pressure exerted by the air in the Earth’s Atmosphere on Earth. Results from collisions of atoms and molecules in air with objects. Depends on altitude and weather. As you climb a mountain, the density of Earth’s atmosphere decreases. What happens to atmospheric pressure? It decreases since there are less particles present to collide with objects.

Barometers A barometer is a device used to measure atmospheric pressure. Some use mercury and a tube. Mercury travelling further up the tube indicates more pressure is being exerted on the mercury, and thus higher atmospheric pressure.

SI unit of pressure is the pascal (Pa), although it represents only a small unit of pressure. Two other units also used. Atmospheres (atm) and Millimeters of mercury (mm Hg)

Converting Between Units of Pressure A pressure gauge records a pressure of 450 kPa. What is this measurement expressed in atmospheres and millimeters of mercury?

Kinetic Energy and Temperature As a substance is heated, initially its particles absorb energy and store it as potential energy. This stored energy does not increase the temperature of the substance. However, the remaining absorbed energy that is not stored speeds up the particles, thus ____________ their potential energy.

Average Kinetic Energy Particles in any collection of atoms or molecules in a given temperature have a wide range of kinetic energies. However, most particles fall in the same range. The average kinetic energy is used to describe the kinetic energy of a sample, and is the same for all substances at a given temperature. Average kinetic energy also explains temperature

Average Kinetic Energy and Kelvin Temperature The Kelvin temperature of a substance is directly proportional to the average kinetic energy of the particles of a substance. Heat is produced by the motion of particles Thus a higher temperature means more kinetic energy (the particles are moving faster). If the particles of a gas stopped moving, what would the Kelvin temperature be?

Assessment According to the kinetic theory, the particles of a gas Are attracted to each other Are in constant random motion Have the same kinetic energy Have a significant volume

Assessment The pressure a gas exerts on another object is caused by The physical size of the gas particles Collisions between gas particles and the object Collisions between gas particles The chemical composition of the gas

Assessment The average kinetic energy of particles in a substance is directly proportional to the Farenheit temperature Kelvin temperature Molar mass of the substance Celsius temperature

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