Kinetic Theory and Exothermic/Endothermic Reactions

Kinetic Theory

Kinetic Theory - A theory concerning the thermodynamic behavior of matter, especially the relationships among pressure, volume, and temperature in gases.

It is based on the dependence of temperature on the kinetic energy of the rapidly moving particles of a substance.

According to the theory, energy and momentum are conserved in all collisions between particles, and the average behavior of the particles can be deduced by statistical analysis.

6 Kinetic Theory of Matter 1)All matter is made up of atoms and molecules that act as tiny particles. 2)These tiny particles are always in motion. 1)State of matter depends on its molecular motion as measured by temperature ↑ temperature = ↑ motion of particles ↓ temperature = ↓ motion of particles

Kinetic Theory of Matter 3) At the same temperature, the heavier particles move slower than the lighter particles. 7

Temperature A measure of the average kinetic energy (K.E.) in a sample. K.E. – Energy of Motion 8

Absolute Zero Temperature at which all molecular (particle) motion stops. 0 Kelvin ( -273 °C; -459 °F) 9

Intermolecular Forces (IF’s) Force of attraction between molecules/particles. Become stronger as molecules get closer together; therefore IF’s are strongest in solids. 10

3 States of Matter - Solid - Liquid - Gas

Basis for classification of the 3 States of Matter - Particle arrangement - Energy of the Particle - Distance between particles

Solids The particles in the solid vibrate around a fixed point. Most solids are crystalline—they have definite repeating structure.

Solids are held together by strong intermolecular (IM) forces.

Substances that have more than one crystalline structure are called allotropes. Carbon can have several allotropes, for example diamonds and coal.

Amorphous solids (like glass) don’t have a definite structure

Melting point is the temperature at which a solid becomes a liquid. As the particles gain kinetic energy, they vibrate and spin themselves right out of their structure.

Freezing point is the temperature at which a liquid becomes a solid. As the particles lose kinetic energy, the intermolecular forces hold the particles together.

The melting point and freezing point of any substance is at the same temperature!!

Liquids In a liquid, particles vibrate and spin as they move from place to place and slide past one another. There are still intermolecular forces holding them together, just not as strong as those of a solid.

Both liquids and gases can flow, but liquids have viscosity. Viscosity is a liquid’s resistance to flow. Syrup has a high viscosity (it is difficult to pour.) Water has a low viscosity.

There are two ways in which a liquid becomes a gas: Evaporation and Boiling

Evaporation — the particles with the highest amount of kinetic energy go from liquid to gas. This is a cooling process, because it lowers the overall Kinetic Energy of the liquid.

Evaporation is the reason why sweat cools your body. The evaporation of a liquid only occurs at the surface of the liquid.

The boiling point is the point at which the internal vapor pressure of a liquid is equal to the external pressure. (It is also a cooling process). Boiling occurs throughout the liquid The boiling point is a function of BOTH temperature AND pressure.

Gases A gas is composed of particles that are small, hard spheres with almost no volume or particle interaction.

Gases Particles in a gas are in constant motion—they travel straight paths unless they collide with another particle or their container.

Gases All collisions are considered elastic—no energy is lost

Gases have the highest kinetic energy. Gases have the weakest intermolecular forces. In a gas particles move very quickly and independently of each other.

Gas Pressure Kinetic theory explains the existence of gas pressure, the force exerted by a gas per unit surface area.

Gas Pressure The force of one molecule hitting an object is relatively small, but the result of billions of particles of air hitting a surface at once is significant.

The absence of particles is called a vacuum. No particles = no pressure Atmospheric pressure is the amount of pressure from the particles in the atmosphere colliding with objects.

Atmospheric Pressure decreases with altitude because the number of air particles decreases with altitude.

Temperature When a substance is heated, the particles speed up, causing faster movement and more collisions. This is a rise in temperature.

Which phase of matter (ice or steam) do you think has the most kinetic energy? The least?

Exothermic and Endothermic Reactions

An exothermic reaction is a chemical reaction that releases energy in the form of heat. Feels HOT. Expressed in a chemical equation: reactants → products + energy

Example mixing water and strong acids

An endothermic reaction is a chemical reaction that requires heat energy in order for the reaction to occur. Feels COLD Expressed in a chemical equation: reactants + energy → products

Example evaporation of water

On the following diagram, determine which line represent a exothermic reaction and which line represent an endothermic reaction.

Use your notes to complete the ‘Kinetic Theory and Exothermic- Endothermic Practice Sheet’ found on LMS. 10 pts. on weekly grade Work on for the remainder of class. Due Monday