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# AP Thermodynamics

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

What is the first law of thermodynamics? | Energy cannot be created or destroyed; it is merely transferred. |

What is the second law of thermodynamics? | In nature, systems will spontaneously move towards a state of greater entropy |

What is the third law of thermodynamics? | The entropy of a pure crystalline substance at absolute zero is zero. |

What is enthalpy? | Heat |

What is entropy? | The craziness, and measure of disorderness? |

When solving for entropy, in comparison to solving for the heat of equation or Gibbs' Free Energy, what must you expect for entropy that is different from the other two? | Entropy wants to be positive |

The most important equation relating to Thermodynamics, and why? | (Delta)G= (Delta)H- T(Delta)S Because it relates all three values, Gibbs, the heat of formation, and entropy in one equation. |

When Gibbs is negative, what is the equation telling you? | The reaction is spontaneous in the forward direction; but, not spontaneous in the reverse direction. |

Why is Hess's Laws used? | Hess's Laws can be used to calculate the heat of formation for many different compounds by using a series of elementary steps, because calculating the total is rather inconvenient. |

What is the equation for calorimetry? What does the "q" stand for? What does the "c" stand for? | q= mc(Delta)T Heat Specific Heat |

What does big "C" mean? | Big C can occupy the space for the mc, in the calorimetry equation. |

What is the difference between Cal and cal? | Calories are what we eat, and are measured in Kilos; calories are simply joules. |

What si the SI unit for energy/heat? | Joules |

What is another way to calculate the heat of formation? | (Bonds broken)- (bonds formed) |

When the specific heat of a substance is high, is more energy needed to heat it up, or less? | When the specific heat of a substance is high, more energy is needed to heat it up, and it will cool much slower. |

Why must we calculate the formation of heat for water, instead of directly going to calculate it for the specific substance? | A specific substance will not tell you the temperature change or the specific heat. We can calculate the energy absorbed by the water, and then negate it. |

When working with entropy, why must you be careful when applying it to other equations that involve Gibbs and the Heat of Formation? | Entropy is small, and it is reported in Joules, not kJ like the other two. The formula must be consistent in terms of units. |

What equation is used to find the amount of work done? | E= q + w Q is the heat, and w is the work |

When is work or heat positive and negative? | When work is done on a system, energy is being absorbed and it will be positive. When the system does work on its surroundings, then work will be negative. |

What is an open system? | An open system allows changes in mass and temperature to occur. Highly inaccurate |

What is a closed system? | A closed system allows changes in temperature to occur, but not in mass. |

What is an isolated system? | An isolated system does not allow changes in mass or temperature, but the excess heat can cause damage to calorimeters. It is the most accurate. |

What law resembles the first law of thermodynamics? | The law of conservation of mass |

Name the scenarious in which entropy of a system will increase | 1. When a solid goes to a liquid, or gas (gases are craziest). 2. Aqueous solutions mean more particles, so more craziness. 3. When more moles are being made. 4. When a polar molecule is formed, there is order, and entropy decreases. |

When using Hess's Law, what must you do? | 1. Use cancellation to check. You should end up with the same equation. 2. When reversing an equation, negate the heat. 3. When you want to divide the amount of moles, divide the heat by the same fraction. 4. When you multiple moles, multiple the heat |