Chapter 6 - Energy + Thermochemistry

What is energy? How many types?

Ability to cause motion/to do work/transfer heat ( in joules/calories)

2 types of energy

• Kinetic Energy

• Potential energy

How many joules in 1 calorie? 1 joule is equal to what?

4.184 Joules → 1 calorie

1 joule → 1 kgm²s^-2

What is the 1st law of thermodynamics?

Law of conservation of energy —

energy can neither be created nor destroyed.

total energy of universe is constant.

-Q lost = Q gained

(2 objects of different temperatures will transfer to a higher → lower temperature until both reach the same temp)

Equation for energy

Q = ms∆t

q - energy

m - mass

s - specific heat (cal g^-1 C^-1 / JgC^-1 )

∆T - change in temp (C or K)

+gain of energy (endothermic process)

-loss of energy (exothermic process)

System

object/group being studied

Surroundings

outside system that can exchange energy w/ system

Work

energy to move an object that has mass

Heat

energy to cause temperature of object to rise

Exothermic process

Energy as heat gained by system and transferred to surroundings

∆H is negative number

• Q is negative when energy removed from system

Endothermic

Energy as heat gained by system through transfer of energy from the surroundings

∆H is positive number

• Q is positive when energy added to system

Enthalpy (H)

energy transferred as heat in systems at constant temperature

∆H = change in enthalpy

What are the rules of enthalpy?

1. Enthalpy changes are specific to reactants/products with amts and states

2. -∆H means energy released as heat by system. ∆H means energy as heat gained by system.

3. If you reverse chem reaction, reverse sign of ∆H

What is Hess’s Law?

If reaction is sum of 2+ more reactions, ∆H for overall process is sum of ∆H values of those reactions.

∆H1 + ∆H2 + ∆H3… = ∆H total

• If you double a reaction, ∆H is doubled

• If you reverse a reaction, ∆H is reversed

What does standard state mean? Elements in standard state are?

Standard State - most stable form of substance in physical state at 1 atm/298K

Element @ standard state is 0

Enthalpy Equation

∆H_rxn = Σ(∆H_f products) - Σ(∆H_f reactants)

• Add up all the ΔH values for products

• Add up all the ΔH values for reactants

• ΔH < 0 → exothermic (releases heat 🔥)

• ΔH > 0 → endothermic (absorbs heat ❄)

Kinetic Energy

Energy of motion depending on mass and speed of moving object/atoms/molecules in chem reaction

KE = ½ mv²

m = mass

v = velocity

Potential Energy

Energy of position; stored energy in chemical bonds

mgh = gravitational potential energy

m = mass

g = 9.8ms^-2 (acceleration due to grav)

h = height

How many electrons do each orbital contain

2 - one must be up and other must be down

What is “n”

Principle quantum number “shell”

• refers to energy level (1 through infinity)

• higher energy lvl, the farther

What is “l”

“angular quantum number”

Refers to shape of orbital

• values: 0 to (n-1)

example: if n=3 then l can be from 0,1,2

What is m_l

“magnetic” quantum number

• direction + orientation of orbital

• -1 → 1

what is m_s

Spin quantum number

• refers to electron spin (up and down)

• values: ½ → -1/2

What does shorter wavelengths and longer wavelengths mean? wb frequency?

Shorter = more energy

Longer = less energy

Higher frequency = more energy

Lower frequency = less energy

What is ROYGBIV

Red, Orange, Yellow, Green, Blue, Indigo, Violet

LOWEST —> HIGHEST energy

LONGER WAVELENGTHS —> SHORTER

LOWER FREQ —> HIGHER

Range of visible light

400 nm to 700 nm

(just do +50nm for each step)