Chemistry Exam 4

Open System

Like an open water bottle, they allow the transfer of matter and energy.

Closed System

Like a closed water bottle, they do not allow transfer of matter, but DO allow transfer of energy.

Isolated System

Do not allow the transfer of either matter nor energy.

State Functions

Variables that define HOW a system starts from HOW it ends. Ask only final-initial functions like ΔH, ΔG, ΔS, ΔU, ΔP, ΔT, ΔV, Δm/Δn, and Δdensity.

Path Functions

Follow the mechanism, or the path, for a given process. Like q and w.

What does ΔH/H represent?

Enthalpy and Change in Enthalpy.

What does ΔG/G represent?

Gibbs Free Energy and change in Free Energy.

What does ΔS/S represent?

Entropy and change in Entropy.

What does ΔU/U represent

Internal Energy and change in Internal Energy.

What does q represent?

Heat.

What does w represent?

Work.

Extensive Properties

Are additive properties of a system like volume, mass, moles, and energy.

Intensive Properties

A property that defines a system. This NOT additive. If you ratio 2 extensive properties, you get out an intensive property.

When something ENTERS the system…

The sign is positive (+).

When something LEAVES the system…

The sign is negative (-).

What is negative when energy LEAVES the system? What about when energy ENTERS the system?

Heat (q) and work (w) are negative when energy leaves, and positive when energy enters.

When ΔH is negative…

System is exothermic.

When ΔH is positive…

System is endothermic.

Heat v. Work

Heat is chaotic energy, while work is a controlled flow of energy. Both are PATH functions, meaning the methods taken to heat something, change volume, etc. WILL affect the outcome!

“Done on surroundings” is the same as…

Work done BY the system, and therefore leaving the system.

“Done on the system” is the same as…

Work done BY the surroundings, and therefore entering the system.

An increase in piston volume does work on the surroundings. Why?

W = P * ΔV, so if ΔV is positive (because piston volume increases), then work is negative, meaning it is done on the surroundings and LEAVES the system.

ΔU_univ = 0 means….

Energy is conserved.

What is the relationship of heat and work to ΔU?

ΔU = q + w.

Relationship of ΔU and work equation to ΔH?

ΔH = ΔU + P * ΔV

What is the source of ALL potential and kinetic energy in a system?

U, or internal energy.

Calorimetry allows ΔU_sys = -ΔU_surr to…

Measure unknown ΔU reactions.

In a bomb calorimeter (closed) system, what is held constant, and how does that affect ΔU?

VOLUME is held constant, so ΔU = q_v because no P * ΔV work.

In a coffee cup calorimeter (open) system, what is held constant, and how does that affect ΔH?

PRESSURE is held constant, so ΔH = q_p.

If the U (internal energy) of the reactants is LESS than the products…

The ΔU is positive because energy is gained via entering the system.

If the U (internal energy) of the reactants is MORE than the products…

The ΔU is negative because energy is lost via leaving the system.

Heat Capacity

Amount of heat (J) to raise temperature by 1 degree. Can be measured in grams or moles.

Equation for Heat Capacity

q = mCΔT or q = nCΔT

If heat added to 2 compounds is the same then…

mCΔT = m₂C₂ΔT

When mass and heat are the same, how do you determine the temperature change?

Via heat capacity value. If larger