Equilibrium Chapter 17

MRE’s The idea behind a flameless heater is to use the oxidation of a metal to generate heat. Magnesium metal works better than iron because it rusts much more quickly. To make a flameless heater, magnesium dust is mixed with salt and a little iron dust in a thin, flexible pad about the size of a playing card. To activate the heater, a soldier adds a little water. Within seconds the flameless heater reaches the boiling point and is bubbling and steaming. To heat the meal, the soldier simply inserts the heater and the MRE pouch back in the box that the pouch came in. Ten minutes later, dinner is served!

How long does a reaction take? The amount of time it takes for a chemical reaction to come to completion can vary depending on the reaction Strike a match and it erupts instantaneously. Coal made from dead plants takes millions of years

Rates Rates measure the speed of any change that occurs within an interval of time. In chemistry, rates of chemical change usually are expressed as the amount of reactant changing per unit time.

Different Reactions Which occurs fastest? Which reaction occurs slowest?

Collision Theory Rates of chemical reactions are related to the properties of atoms, ions, and molecules through a model called collision theory. According to collision theory, atoms, ions, and molecules can react to form products when they collide, provided they have enough kinetic energy.

Think clay If you throw 2 clay balls together gently, they do not stick together, kinda like the lack of reaction between colliding particles with low energy. If you throw the same balls of clay together with great force, they stick together.

Collision Theory Furthermore, molecules must collide with the correct orientation and with enough energy to cause bond breakage and formation.

Activation Energy Activation energy is a barrier that reactants must cross to be converted to products.

Activated Complex An activated complex is the arrangement of atoms at the peak of the activation-energy barrier Also called transition state.

Factors Affecting Reaction Rates Temperature Concentration Particle Size Catalysts Pressure

Temperature Usually, raising the temperature speeds up the reactions, while lowering the temperature slows down the reactions. This will increase the number of particles that have enough kinetic energy when they collide.

Concentration Cramming more particles into a fixed volume increases the concentration of reactants.

Particle Size The smaller the particle size, the larger the surface area for a given mass of particles. Which burns faster, a piece of wood or a kindle? Why?

Catalyst A catalyst is a substance that increases the rate of a reaction without being used itself. Catalyst permit reactions to proceed at a lower energy than required.

Reversible Reaction Do reactions only go one way or do reactions go 2 ways? Let’s look at this equation: 2SO2(g) + O2 ---- 2SO3 What happens when sulfur dioxide and oxygen gas are mixed in a sealed container? -----------

Reversible Reactions As the SO3 concentration increases, a small amount slowly reverts to SO2 and oxygen by the reverse direction! As the concentration of SO3 becomes higher and higher, the reverse reaction speeds up! Eventually SO3 decomposes to SO2 and O2 as fast as it forms SO3.

Chemical Equilibrium Equilibrium occurs when opposing reactions occur at equal rates. Reactants and products are not necessarily equal in amount.

Le Chatelier’s Principle If a stress is applied to a system in dynamic equilibrium, the system changes to relieve stress. Stresses include changes in the concentration of reactant or products, changes in temperature, and changes in pressure