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# Physics A

### Formulas

Question | Answer |
---|---|

What is the formula for internal energy? And the first law of thermodynamics? | dU = Q + W |

What is internal energy equal to? | dEth + dEbond + dEatomic + dEnuclear |

What is the formula for entropy, not at constant pressure? | H = U + PV |

What is the formula for change in entropy at constant pressure? | dH = Q |

What is the exact formula for work? Approximate formula for work? | W = -der PdV or W = appx Pavg dV (at constant pressure) |

What is the formula to calculate Q when there is no phase change? | Q = deriv CdT or appx: CdT |

What is the equation for the ideal gas laws? | PV = nRT |

What does Q represent? | Q = Ebond + Etherm |

What is the formula for entropy when the number of microstates is known? | S = kb lnOmega |

What is the entropy for the system? | dS = Q/T |

What is the formula for heat capacity? | C = Q/dT |

What is the formula for the heat capacity at constant volume? | Cv = dEth/dT (if Q = Etherm) |

What is the formula for the heat capacity at constant pressure and in the ideal gas model? | Cp = Cv + R |

What is the formula to calculate Etherm for a specific phase or number of molecules? | Etherm = (#modes/molecule)(1/2) nRT |

What is the formula for Etherm when the number of modes is known? | Etherm/mode = (1/2)(Kb) T |

What is the formula for Etherm when the number of moles is known? | Etherm/mole = Na (#modes/molecule) (1/2)(Kb)T |

What is the formula to calculate Etherm for a particular substance? | Etherm = CdT |

How do you calculate Ebond? | Either add all the Ebond numbers together or refer to the PE on the pair wise graph |

How do you calculate Ebond during a phase change? | abs val Ebond = abs val (dMdHmelt) or abs val (dMdHvap) |

What is the formula to calculate the change in kinetic energy? | dKE = (1/2)m dV^2 |

What is the formula to calculate the change in gravitational potential energy? | dPEgrav = mgdy |

What is the formula to calculate the change in spring potential energy? | dPEspring = (1/2)k dx^2 |

What number is represented by Na? | Avogadro's number |

What number is Kb represented by? | 1.38 x 10^-23 J/K |

What number is R represented by? | Na x Kb = 8.31 J/Kxmol |

How much does the mass change during a phase change? | dm = Q/dH |

How much does the temperature change during a phase change? | dT = Q/dH |

How do you calculate the kinetic energy of a spring mass? | KEsping-mass = (1/2)mv^2 |

How do you calculate the potential eneryg of a spring mass? | PEspring-mass = (1/2)ky^2 |

How do you calculate the magnitude of the attractive or repelling forces between two adams? Think pair-wise | absval F = absval d(PE)/dr |

How do you calculate the intermolecular Ebond between adams? | -(total number of n-n pairs) x epsilon |

How do you calculate the Etherm total? | (total number of active modes) x (1/2)KbT |

In a closed system what is the Entropy? | dS is greater than or equal to 0 |

How do you calculate the number of modes? | Estimate the number of modes then the formula is (#modes/atom)(#atoms) |