Chemistry Chapter 5 - to remember

Order of SI units

tera	T	10¹²
giga	G	10⁹
mega	M	10⁶
kilo	k	10³
hecto	h	10²
deca	da	10¹
deci	d	10⁻¹
centi	c	10⁻²
milli	m	10⁻³
micro	µ	10⁻⁶
nano	n	10⁻⁹
pico	p	10⁻¹²
femto	f	10⁻¹⁵

Equation for heat capacity (C)

𝐶=𝑄/Δ𝑇

Specific heat capacity (J/g^oC, J/g^oK)

q = m C_s Δ𝑇

Molar heat capacity

q = n C_m Δ𝑇

Energy Change for a system. The sum of energy transferred as heat and work.

ΔU/ΔE = q + w

Internal energy

ΔE_system = KE+PE

Signs (from systems point of view)

Quantity	Sign	Direction of energy flow	Process type / example
q	+
q	−
w	+
w	−

Quantity	Sign	Direction of energy flow	Process type / example
q	+	Heat flows into the system	Endothermic (ice melting, KNO₃ dissolving)
q	−	Heat flows out of the system	Exothermic (combustion, KOH dissolving)
w	+	Work done on the system	Compression (gas squeezed by a piston)
w	−	Work done by the system	Expansion (gas pushing a piston out)

Signs for energy change of a system

q	w	ΔE
+	+	+ (system gains energy)
−	−	− (system loses energy)
+	−	Depends: + if
−	+	Depends: + if

Quick tip: the two “depends” cases are the ones to compare magnitudes on. Whichever of q or w is larger in size decides the sign of ΔE.

Work

w = −P_ext · ΔV

Enthalpy (H) is…

change in energy of a system at constant pressure (ΔE) or the sum of the change in internal energy and PV product (H = E + PV)

positive in an endothermic reaction

negative in an exothermic reaction

in KJ/mol

equal to heat exchanged (ΔH = Δq_rxn)

Coffee-Cup Calorimeter equations

q _solution = -q_rxn

q_rxn = ΔH_rxn (moles)

q_rxn = ΔH_rxn (mass) if units are in kJ/g