Unit Thirteen Chemical Equilibrium A few terms Chemical

Unit Thirteen Chemical Equilibrium

A few terms… �Chemical Equilibrium • When forward and reverse reactions are occurring under the same conditions and at the same rate �Static • At rest; not changing �Steady State • Constant change but unlike equilibrium there is no reverse reaction

Determine whether the following are in “equilibrium” or “steady state” � An open pan of water is boiling on a stove. The temperature of the water is constant. • Steady state �A balloon contains air and a few drops of water. The pressure in the balloon in constant. • Equilibrium �A colony of ants are going about their daily routine in an anthill. The population of the anthill is constant. • Equilibrium

Determine whether the following are in “equilibrium” or “steady state” �A Bunsen burner burns in the lab to give a well-defined flame. Supplies of gas and air are constant. • Steady state �A line of Chi-Hi students at the pop machine. Every time money goes into the machine, a can of pop comes out. • Steady state

Rate of a Chemical Reaction �A measure of how fast the reaction proceeds � If the rate is fast, a large amount of reactants are being converted to products. � If the rate is slow, a small amount of reactants are being converted to products. � Reaction rates can be controlled if we understand the factors that influence them.

Collision Theory �Chemical reactions occur through collisions between molecules or atoms �High energy collisions lead to products and low energy collisions do not. • This is because of the activation energy �Activation energy – the energy required to begin to break these bonds

Concentrations Effects on the Rate of Reaction �The rate of a chemical reaction generally increases with increasing concentration of the reactants. �As the reaction proceeds, there are fewer reactant molecules (because they have turned into products) and the reaction slows down.

Temperature Affects the Rate of Reaction �The rate of a chemical reaction generally increases with increasing temperature of the reaction mixture. �Raising the temperature makes the molecules move faster therefore they experience more collisions pre unit time, resulting in faster reaction rates.

Dynamic Equilibrium � Reversible reaction – a reaction where the products can reform reactants • i. e. ice • A reaction that can proceed in the forward and reverse direction � Irreversible reaction • Burning paper � Dynamic – one-way reactions Equilibrium – the condition in which the rate of the forward reaction equals the rate of the reverse reaction

Dynamic Equilibrium �At dynamic equilibrium the rates of the forward (left to right) reaction and the reverse reactions are equal • The forward and reverse reactions do not stop; they are in a dynamic system • Proof: A broken crystal in a saturated solution will repair as the crystal is dissolving and forming a precipitate at the same time

Characteristics of a System at Equilibrium � No change in observable properties � Changes � Rates equal take place at the molecular level of forward and reverse reactions are � Equilibrium conditions can change (but the system will adjust to again be at equilibrium)

At dynamic equilibrium the forward and reverse reaction rates are the same. Since the rates are the same, the concentrations are no longer changing. However, just because the concentrations of the reactants and products no longer change at equilibrium, does not imply that the concentrations of reactants and products are equal to one another at equilibrium.