IGCSE Chemistry: Specimen Questions with Answers 210 - 211 of 240

Question number: 210

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

  1. 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.

Question number: 211

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Malonic acid is a white crystalline solid which is soluble in water. It melts at 135 °C. The structural formula of malonic acid is given below. It forms salts called malonates

Molecular formula of malonic acid is .

When malonic acid is heated there are two products, carbon dioxide and a simpler carboxylic acid. Deduce the name and molecular formula of this acid.

[2 Marks]

Explanation

This acid melts at . , and at a higher temperature it rapidly decomposes into acetic acid and carbon dioxide and formula of this acid is and name is acetic acid.