IGCSE Chemistry: Specimen Questions with Answers 209 - 210 of 240

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Question 209

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Substances can be classified as:

Elements can be divided into:

Define each of the following terms:

mixture

[1 Marks]

Explanation

a compound is a substance that results from a combination of two or more different chemical element s, in such a way that the atom s of the different elements are held together by chemical bonds that are difficult to break.

Question 210

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One of the factors which determine the reaction rate of solids is particle size.

A mixture of finely powdered aluminum and air may explode when ignited.

An explosion is a very fast exothermic reaction. This causes a large and sudden increase in temperature.

Explain each of the following in terms of collisions between reacting particles.

Explain why for most reactions the rate of reaction decreases with time.

Explanation

The rate of a chemical reaction is dependent on the concentration of the reagents. … The reason we care about this is that over the course of a reaction the concentration of the reagents decreases. This is because the reagents, over time, are getting used up in order to make the products.

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