A Taste of Thermodynamics and Reaction Rates

Nature of Energy

• Energy – the ability to do work or produce heat.

Two basic forms of energy

Potential – stored energy

Kinetic - energy of motion

Law of Conservation of Energy

• Energy can be converted from one form to another, but can not be created or destroyed. Also known as the 1 st law of Thermodynamics.

Heat versus Temperature

• Temperature is an indication of the kinetic energy of an object. It also lets you know which way the energy will flow in relation to the surrounding objects.

If an object has a higher temp than its surrounding, energy will flow out of the object to the surroundings.

If an object has a temp lower than its surroundings, energy will flow into the object.

Heat

• Heat is the measure of the amount of energy.

• A Calorie is the metric unit of heat. It is the amount of heat needed to raise the temperature of one gram of water one degree Celsius.

• The SI unit is a Joule.

• 1 calorie = 4.184 Joules

• Specific Heat- the amount of heat needed to raise the temperature of one gram of that substance one degree celsius.

• A dietary Calorie, with a capital “C” is actually a Kilocalorie.

• So a 2000 Calorie diet is really a 2,000,000 calorie diet.

• So how do we measure Calories?

Calorimeter

• Because we know the definition of a calorie, the mass of the water in the calorimeter and the temperature change. We can calculate the number of calories produced.

• q = c x m x ∆T The way the book writes it. I prefer

• ΔH = c x m x ΔT

• Because you can’t really measure heat content, only the heat change. I like

• ΔH as change in heat.

• C is the specific heat of water.

• M is the mass of the water.

• ΔT is the change in temperature.

• See sample problem on page 524

Heat of Reaction

• Remember Heat of solution from last chapter?

• Heat of reaction is just like it, the energy change that takes place during a chemical reaction.

• (+) heat of rx = endothermic

• (-) heat of rx = exothermic

Potential Energy Diagram

Potential Energy Diagram II

Note: relate to heat and cold packs

Rates of reaction

• How fast or how slow a reaction proceeds.

• This can be explained using a model called the Collision Theory

Collision Theory

• Like two cars in a very large parking lot slowly and randomly moving around.

• What is the likely hood that they will react with each other?

• They have to find each other, make contact, which is hard enough, and at the correct orientation to cause an accident that will exceed the insurance deductible

• (threshold energy)

How can we increase the odds of an accident happening?

• Increase the number of cars ( concentration ) list various factors

increase the speed, (temperature) bigger cars, more surface area is easier to

hit.how well the vehicles are made a preus versus a BMW (nature of reactants)

Demos would be good

Particle energy & Temperature

Activation energy (threshold)

Catalysta farmers inventory

• A substance that speeds up a reaction, but is not affected by the reaction.

• A chemical instigator

Energy of reaction