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问题 选择题

（2011年湖北荆门，6题）下列过程中，不是化学变化的是：（   ） 

A．铁锅生锈

B．煤气燃烧

C．石蜡熔化

D．大米酿酒

答案

答案：C

化学变化是指生成了其它物质的变化，其特征是有新物质生成．

A、在铁锅生锈过程中，铁、氧气、水变成了铁锈，有新物质生成，是化学变化，所以错误．

B、在煤气燃烧过程中，一氧化碳和氧气变成了二氧化碳，有新物质生成，是化学变化，所以错误．

C、在石蜡熔化过程中，只是石蜡的状态发生了变化，没有新物质生成，是物理变化，所以正确．

D、在大米酿酒过程中，糖类变成了酒精，有新物质生成，是化学变化，所以错误．

故选C．

点评：物理变化与化学变化是初中化学最基本的概念，是考查的热点之一，正确理解定义，明确二者的本质区别：是否有其它物质生成，是解题的关键所在．

填空题

下图一表示某绿色植物细胞内部分代谢活动的相互关系，其中a、b、c代表不同的细胞器，①～⑤代表不同的物质。请据图回答问题：

 

图三表示一昼夜(0时至24时)在一个种植有番茄植株的密闭容器内O2相对含量的变化，据图分析：

①番茄植株光合作用释放的O2量和呼吸作用消耗的O2相等的点是（）。

②该番茄植株经过一昼夜后，是否积累了有机物（），理由是（）。
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