Chem exam 2

What does the sign of work (w) mean?

--w (Expansion): Work done by the system on surroundings; occurs when \Delta V > 0 or moles of gas increase$(\Delta n_{\text{gas}} > 0).$

+w (Compression): Work done on the system by surroundings; occurs when \Delta V < 0 or moles of gas decrease $(\Delta n_{\text{gas}} < 0).$

What does the sign of heat (q) mean?

-q (Exothermic): Heat flows out of the system to surroundings.

+q (Endothermic): Heat flows into the system from surroundings.

What does the sign of heat (q) mean?

-q (Exothermic): Heat flows out of the system to surroundings.

+q (Endothermic): Heat flows into the system from surroundings.

How to find delta H rxn for two reactions

cancel out a compound by changing equations

then add their delta H’s

change of energy equation

delta E = q + w

Work equation

W = -P * delta V

how much is 1 cal

4.184 J

Enthalpy equation

delta H = $-q/moles$

Enthalpy < 0

exothermic

enthalpy > 0

endothermic

conversion factor for thermo

$$\frac{change of enthalpy in reaction{}}{\# of moles of reaction{}}$$

speed of light equation

$$c=\lambda v$$

c=3×$10^8$

$$\lambda$$

wavelength

v

frequency

Energy equation

E=hv and E =(hc/$\lambda$)

Rydberg formula

$$\frac{1}{\lambda}=R\left(\frac{1}{n1^2}+\frac{1}{n2^2}\right)$$

n2>n1

How can delta H of rxn be changed?

multiply reaction → multiply delta H

reverse reaction → flip sign of delta H

Photon Energy / Bohr Model Energy Equation

standard state?

25 C

1 atm

What is $\Delta H^\circ_f$and howdo you use it to calculate the enthalpy of a reaction$(\Delta H^\circ_{\text{rxn}})?$

\ Definition: Standard Enthalpy of Formation. 

Reaction Formula:

$$Delta H°rxn = Σ [n × Delta H°f (products)] - Σ [m × Delta H°f (reactants)]$$

Crucial Step: Multiply each compound's$\Delta H^\circ_f$value by its stoichiometric coefficient (number of moles) from the balanced equation!

Conversion factor from 1 L•atm to Joules

h

plank’s constant- 6.63 × 10^-34 m²kg / s

$$\gamma^2$$

spaci energy = probability density

The Four quantum numbers

Electromagnetic radiation and waves

What are the electron configuration exceptions for Chromium (\text{Cr}) and Copper (\text{Cu})? 

Half-filled and fully-filled d-subshells provide extra stability.

How do you distinguish between Core, Outer, and Valence electrons?

Core electrons: Inner electrons represented by noble gas cores. 

Outer electrons: Electrons in the highest energy level$(\text{highest } n)$

Valence electrons: Outer electrons. 

Transition metals:

$$\text{Valence } e^- =\text{outer}$$

$e^- + \text{number of } d\text{-electrons}.$ $(Some d\text{-electrons}$ may be bonded).

How does atomic size change across periods and down groups on the periodic table?

Pauli Exclusion

Hund’s Rule

Aufbau principle