Chemistry

Heat

The flow of energy due to the temperature differences. Energy always travels from high energy (high temperature) to low energy (low temperature). Heat energy is represented as a Q. Heat is measured in Joules, Calories or KiloCalories.

Temperature

A measure of the average kinetic energy of the components of a substance. Increasing the temperature increases the rate of the reaction. Increase in temperature causes an increase in kinetic energy. So if the particles are moving at a faster pace, more collisions take place.

Law of Conservation Energy

Energy can be converted from one form to another but cannot be created or destroyed. Ex: Energy frequently changes from potential to kinetic energy.

Kinetic Energy

Energy due to motion, it depends on the mass and velocity (speed) of the object.

What is Energy?

Energy is the thing that keeps you moving. Power, force and velocity. Something that fuels people. Charge, Positive/Negative, Movement, ATP.

Calorie (cal)

Energy needed to raise 1g of H2O by 1 degrees Celsius. 1 cal = 4.184 J

Solution Equilibrium

Rate of dissolving equals the rate of crystallization. When this happens, you have a saturated solution.

Reversible Reactions

Reactions in which the products can regenerate the original reactants. Ex: 2SO2 (g) + O2 (g) -- 2SO3 (g).

Factors that Affect the Rate of a Reaction

1. Catalyst 2. Concentration 3. Temperature 4. Surface Area 5. Nature of Reactants

Important Facts About Equilibria

1. Equilibrium is dynamic 2. Equilibrium most occurs in a closed system 3. Equilibrium can only exist in reversible reactions. The reaction cannot go to completion. 4. Reaction rates are equal but not necessarily the amount of the reactants and/or products

How can we increase the number of effective collisions?

1. Increase reactants 2. Decrease Volume 3. Increase temperature 4. Increase pressure 5. Increase exposed surface

At the freezing point and boiling point, their is no change in temperature.

1. Instead we Use Q = mHf or Q = mHv 2. Hf = Heat of fusion (solidifying/melting) 3. Hv = Heat of vaporization (boiling / condensing)

Nature of the Reactants

A reaction that involves the smallest (least) amount of bond rearrangement (breaking and making new bonds) is fast. Solutions of iconic substances react fast (ions just move close to each other and collide at any angle.)

Activated Complex

A very unstable (high energy) substance formed in the middle of a chemical reaction.

Specific Heat Capacity

Amount of energy required to change the temperature of 1g of a substance by 1 degrees Celsius.

Chemical Equilibrium

Rate of the forward reaction equals the rate of the reverse reaction. Concentration of the products and reactants remains constant. Haber Process: N2 (g) + 3H2 (g)---- 2NH3 (g)

Endothermic Reaction

Endothermic processes take in heat (thermal energy) from the surrounding environment. Heat is absorbed by the reaction, meaning that heat goes into the reaction. When this happens, the temperature drops and it feels cold. Ex: When NH4Cl is dissolved in water, the temperature drops because the salt takes energy from the water to break it up. Energy is absorbed from the surroundings. As a result, the temperature of the surroundings drops.

Endothermic Heat of Reaction

Endothermic reactions have a positive change in temperature. Endothermic reactions take more heat than is released. The products are higher than the reactants.

Exothermic Energy

Exothermic processes release heat (thermal energy) to the environment. This is the opposite of an endothermic reaction. Energy is released into the surroundings as heat. As a result, the temperature of the surroundings increase. Heat is released by the reaction, meaning that heat goes out of the reaction. When this happens, temperature rises and it feels warm. Ex: When NaOH is dissolved in water, it releases energy into the water which makes the temperature of the water go up. Energy is released into the surroundings as heat. As a result, the temperature of the surroundings increases.

Collision Theory

For a reaction to happen, the particles must have sufficient energy and collide at the proper orientation.

Successful Reactions

For a reaction to occur, effective collisions must occur between the reactants.

Exothermic Heat of Reaction

Have a negative change in temperature. Exothermic reactions take more heat than they need to get started. The products are lower than the reactants.

Enthalpy

Heat can be written as a product or reactant. As a product, it indicates an exothermic reaction. As a reactant, it indicates an endothermic reaction.

Remember

Heat is not Temperature. Enthalpy, Delta H is the total heat content of a system.

Surface Area

Increasing the surface area will increase the rate of a reaction. The larger the surface area, the more exposed particles that can react. The more collisions and the faster the rate.

Catalyst

Lowers the activation energy and makes a faster reaction by providing an alternate route.

What is conserved during a chemical reaction?

Matter and energy

Phase Equilibrium

Occurs at the same rate! Rate of melting equals the rate of freezing. Rate of evaporation equals the rate of condensing.

Q = mc^T

Q = energy lost or gained M = mass (g) c = specific heat capacity Delta T = change in temperature

Keep in Mind

Remember that energy is conversed. The energy released by the system is absorbed by the surroundings. Ex: When ice melts, the ice is taking in energy from the air. This means the air is losing the same amount of energy that is gained by the ice.

Joule (J)

Sl (International System of Units). Unit of energy.

Types of energy

Solar, Sound, Kinetic, Nuclear, Gravitational, Electromagnetic, Wind, Potential, Mechanical, Thermal and Light.

Potential Energy

Stored energy or energy due to composition

Heat of Reaction

The amount of heat given off or absorbed in a chemical reaction. Heat of Reaction is the difference in potential energy of the products and the reactants. Delta H = PE products - PE reactants

Heat of Fusion (Hf)

The amount of heat needed to change 1g of a solid into liquid at the normal melting point.

Heat of Vaporization (Hv)

The amount of heat needed to change 1g of liquid into gas at the normal boiling point.

Activation Energy

The smallest amount of energy needed to start a reaction

Temperature Scales

We measure temperature in Celsius, Fahrenheit and Kelvin. In science we use Celsius or Kelvin. Fixed points on the temperature scale are the melting and boiling point of water. (273 K and 373 K respectively)

Increase Reaction Rule

We need to increase the number of effective collisions.

Concentration

When the concentration of one or more of the reactants increases, the rate of the reaction increases (the concentration increases, the number of collisions increases). With gases, increasing pressure gives you an increase in concentration therefore you will get an increase in the rate of the reaction.

Equilibrium

When the forward and reverse reactions occur at the same rate. The rates are equal but the amounts of the reactants and the products are constant.

Energy

the ability to do work to produce heat