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  • 训练标准热标准热量

    The Hope Diamond displayed in a case, showcasing its unique clarity and color.

    Is the Hope diamond just a very expensive pencil?
    ::希望钻石只是个非常昂贵的铅笔吗?

    The Hope diamond is a very expensive piece of jewelry, currently worth about $350 million. A pencil can be purchased for less than a dollar. Both items contain carbon, but there is a big difference in how that carbon is organized. The diamond was formed under very different reaction conditions than the graphite, so it has a different of formation.
    ::希望钻石是一个非常昂贵的首饰,目前价值约为3.5亿美元。 铅笔可以用不到一美元的价格购买。 两种物品都含有碳,但碳的构成方式却有很大的不同。 钻石的形成与石墨的反应条件非常不同,因此其形成方式也不同。

    Standard Heat of Formation
    ::训练标准热标准热量

    A relatively straightforward is one in which are combined to form a . Sodium and chlorine react to form sodium chloride (see video below). Hydrogen and oxygen combine to form water. Like other reactions, these are accompanied by either the absorption or release of heat. The standard heat of formation   ( Δ H f ∘ ) is the change associated with the formation of one mole of a compound from its elements in their standard states. The standard conditions for thermochemistry are 25°C and 101.3 kPa. Therefore, the standard state of an element is its state at 25°C and 101.3 kPa. For example, iron is a solid, bromine is a , and oxygen is a under those conditions. The standard heat of formation of an element in its standard state is by definition equal to zero. The  Δ H f ∘ = 0 for the diatomic elements, H 2 (g), N 2 (g), O 2 (g), F 2 (g), Cl 2 (g), Br 2 (l), and I 2 (g). The graphite form of solid carbon is its standard state with Δ H f ∘ = 0 , while diamond is not its standard state. Some standard heats of formation are listed in  Table .
    ::相对直截了当的一种反应是结合形成一种氯化钠的。 钠和氯反应(见下文视频) 氢和氧结合形成水。 与其他反应一样, 这些反应包括吸收或释放热量。 标准形成热量( Hf) 的标准热量( Hf) 是与其标准状态中某一化合物元素形成一个摩尔相关的变化。 热化学的标准条件为25°C和101.3千帕。 因此, 一个元素的标准状态是其25°C和101.3千帕的状态。 例如, 铁是固体的, 溴是一种, 氧是这些条件下的一种。 标准状态中某一元素形成的标准热量为零。 用于对原子元素的 H2( g)、 N2(g)、 O2(g)、 F2(g)、 Cl2( 2(g)、 2/g)、 Brl 和 I2( g) 。 固体碳的石墨形式是其标准状态, 其标准状态为 Hf0, 而钻石不是其标准状态。 表列出了某些标准形成热量。

    Watch this video of the reaction between sodium metal and chlorine gas.
    ::观看这段关于金属钠和氯气反应的录像。

     

     

    Standard Heats of Formation of Selected Substances
    Substance Δ H f ∘ (kJ/mol) Substance Δ H f ∘   (kJ/mol)
    Al 2 O 3 (s) -1669.8 H 2 O 2 (l) -187.6
    BaCl 2 (s) -860.1 KCl(s) -435.87
    Br 2 (g) 30.91 NH 3 (g) -46.3
    C (s, graphite) 0 NO(g) 90.4
    C (s, diamond) 1.90 NO 2 (g) 33.85
    CH 4 (g) -74.85 NaCl -411.0
    C 2 H 5 OH(l) -276.98 O 3 (g) 142.2
    CO(g) -110.5 P(s, white) 0
    CO 2 (g) -393.5 P(s, red) -18.4
    CaO(s) -635.6 PbO(s) -217.86
    CaCO 3 (s) -1206.9 S(rhombic) 0
    HCl(g) -92.3 S(monoclinic) 0.30
    CuO(s) -155.2 SO 2 (g) -296.1
    CuSO 4 (s) -769.86 SO 3 (g) -395.2
    Fe 2 O 3 (s) -822.2 H 2 S(g) -20.15
    H 2 O(g) -241.8 SiO 2 -859.3
    H 2 O(l) -285.8 ZnCl 2 -415.89

     

     

    Summary
    ::摘要

    • The standard heat of formation is defined.
      ::标准形成热是界定的。

    Review
    ::回顾

    1. What is the standard heat of formation for an element?
      ::元素的标准形成热是多少?
    2. Does the standard heat of formation for water differ in the gaseous and liquid states?
      ::水的标准形成热在气体和液体状态上是否有所不同?
    3. What are temperature and pressure conditions for determining standard heat of formation?
      ::确定标准形成热的温度和压力条件是什么?