Thermodynamics Flashcards

Flashcards about Thermodynamics

What is Thermodynamics?

The study of energy changes and the laws governing the conversion of heat into other forms of energy.

What are the four types of Internal Energy (E)?

electronic, rotational, vibrational, translational

What does the 'system' refer to?

reactants and products represented by the chemical equation

What are 'surroundings'?

all matter around the system that either absorbs or releases thermal energy

What is an exothermic reaction?

The release of thermal energy to an object’s surroundings (temperature of surroundings increases)

What is an endothermic reaction?

The absorption of thermal energy from an object’s surroundings (temperature of surroundings decreases)

What is a State Function (State Variable)?

a property that depends on the current “state” of a system, independent of the pathway taken to reach the state

What are the sign conventions that apply to most state functions?

-∆H means energy leaving the system, +∆H means energy entering the system, - ∆V means volume of system is decreasing, +∆V means volume of system is increasing, -∆n means a decrease in the total # of moles of gas, +∆n means a increase in the total # of moles of gas

What is a Pathway Dependent Function (a.k.a. Process Variable)?

Dependent on the pathway taken to reach the current state; Include work (w) & heat (q)

What is the First Law of Thermodynamics?

Energy cannot be created or destroyed. It can be converted from one form to another.

What is the relationship between Internal Energy, Heat & Work ?

∆E = q + w

What is the formula for calculating Pressure-Volume Work (w)?

w = -P∆V

What is the Ideal Gas Law?

PV = nRT

With Ideal Gas Law, what does ∆E equal?

∆E = q - ∆nRT

When heat is absorbed or released from a system and P is constant, what is the heat released or absorbed equal to?

qP = ∆H

What are Standard Conditions?

conditions of 25oC, 1 atm pressure for gases, 1 mol/L concentration for aqueous species and the physical state or phase the substance exists at under these conditions.

What is Hess’s Law of Heat Summation?

∆H target = ∆H1 + ∆H2 +∆H3 + … = ∑ ∆H known

What are the rules for Writing Formation Equations?

write only one mole of product, reactants in their standard states, choose coefficients to give a balanced equation with only one mole of product

What is the formula to find ∆H using Heats of Formation?

∆H = ∑n∆Hf o (products) - ∑n∆Hf o (reactants)

What is the Relationship Between Bond Length & Bond Energy?

Bond length increases with the atomic radius of each atom involved in a bond. Greater bond length results in a weaker bond… and a smaller average bond energy.

What is Bond Energy?

The enthalpy change required to break a given bond in one mole of gaseous molecules.