问题 选择题

下列生活中的现象从物质变化的角度分析,主要体现化学变化的是

A.酒精挥发

B.食物腐烂

C.家庭自制冰块

D.石蜡受热熔化

答案

答案:B

化学变化是指有新物质生成的变化,物理变化是指没有新物质生成的变化,化学变化和物理变化的本质区别是否有新物质生成.

解:A、酒精蒸发只是酒精分子挥发,状态改变了,没有产生新物质,是物理变化,故A错误;

B、食物腐烂是食物与空气中的氧气发生氧化反应生成新物质而变质,是化学变化,故B正确;

C、家庭自制冰块,水变成冰,只是水的三态变化,没有生成新物质,是物理变化,故C错误;

D、石蜡熔化的过程中只是状态发生改变,没有新物质生成,是物理变化,故D错误;

故选B.

此题是考查化学变化和物理变化的区别,如果没有新物质生成就属于物理变化,如果有新物质生成就属于化学变化,因此关键是看有无新物质生成.

单项选择题
单项选择题

In a recent survey, Garber and Holtz concluded that the average half-hour children’s television show contains 47 violent acts. When asked about the survey network television executive Jean Pater responded. "I sure as heck don’t think that Bugs Bunny’s pouring a glass of milk over a chipmunk’s head is violence. " Unfortunately, both Garber and Holtz and Pater beg the question. The real issue is whether children view such acts as Violence.

The violence programming aimed at children almost always appears in the context of fantasy. Cartoon violence generally includes animation, humor, and a remote setting. There is no evidence of direct imitation of television violence by children, though there is evidence that fantasy violence can energize previously learned aggressive response such as a physical attack on another child during play. It is by no means clear, however, that the violence in a portrayal is solely responsible for this energizing effect. Rather, the evidence suggests that any exciting material can trigger subsequent aggressive behavior and that it is the excitation rather than the portrayal of violence that instigates or energizes any subsequent violent behavior. "Cold" imitation of violence by children is extremely rare, and the very occasional evidence of direct, imitative associations between television violence and aggressive behavior has been limited to extremely novel and violent acts by teenagers or adults with already established patterns of deviant behavior. The institutional effect means, in the short term, that exposure to violent portrayals could be dangerous if shoaly after the exposure (within 15 to 20 minutes), the child happens to be in a situation that calls for interpersonal aggression as an appropriate response, for example, an argument between siblings or among peers. This same institutional effect, however, could be produced by other exciting but nonviolent television content or by any other excitational source, including, ironically, a parent’s turning off the set.

So there is no convincing causal evidence of any cumulative instigational effects such as more aggressive or violent dispositions in children. In fact, passivity is a more likely long term result of heavy viewing of television violence. The evidence does not warrant the p conclusions advanced by many critics who tend to use television violence as a scapegoat to draw public attention away from the real causes of violence—causes like abusive spouses and parents and a culture that celebrates violence generally.

If there is an argument between siblings one hour after their watching some TV violence, these children would ().

A. likely fall into a state of total passivity to their parents

B. likely behave less aggressively than on other occasions

C. unlikely resort to any violent actions but keep peaceful

D. unlikely be more violent than without watching the program