1.
Reactions eventually stop. What is generally the reason for this?
Correct Answer
C. One or more of the reactants has been used up.
Explanation
Reactions eventually stop because one or more of the reactants have been used up. Reactants are the substances that undergo a chemical change during a reaction, and once they are completely consumed, the reaction can no longer proceed. When reactants are depleted, there are no more molecules available to collide and react with each other, leading to the cessation of the reaction.
2.
Marble reacts with hydrochloric acid to produce calcium chloride, water, and carbon dioxide. In which of these mixtures is the rate of reaction likely to be the greatest?
Correct Answer
B. 1g of powdered marble in 100cm3 of hydrochloric acid at 30°C.
Explanation
The rate of reaction is likely to be the greatest in the mixture of 1g of powdered marble in 100cm3 of hydrochloric acid at 30°C. This is because increasing the temperature generally increases the rate of a chemical reaction, as it provides more energy for the reactant particles to collide and react. Additionally, using powdered marble instead of marble chips increases the surface area of the reactant, allowing for more collisions between the particles and further increasing the rate of reaction.
3.
Manganese dioxide is a black powder that catalyzes the breakdown of hydrogen peroxide to water and oxygen. Which of the following statements is correct?
Correct Answer
A. The mass of manganese dioxide will stay the same during the reaction
Explanation
During a catalyzed reaction, the catalyst itself remains unchanged and is not consumed in the reaction. Therefore, the mass of manganese dioxide, being the catalyst in this case, will stay the same during the reaction. The catalyst provides an alternative pathway for the reaction, lowering the activation energy required for the reaction to occur. This allows the reaction to proceed at a faster rate without being consumed in the process.
4.
Which of the following statements about collisions is correct?
Correct Answer
C. Reactions can happen if the colliding particles have enough energy
Explanation
Reactions can happen if the colliding particles have enough energy. This statement is correct because for a reaction to occur, the colliding particles must have enough energy to overcome the activation energy barrier. If the particles have sufficient energy, they can break the existing bonds and form new ones, resulting in a chemical reaction. Therefore, the energy of the colliding particles is crucial for reactions to take place.
5.
The rate of reaction increases as the temperature increases. Which of the following statements provides the best explanation for this?
Correct Answer
B. At higher temperatures the particles have more energy, move faster and collide more often
Explanation
At higher temperatures, the particles in a reaction have more energy and move faster. This increased energy and movement make it more likely for the particles to collide with each other. Since collisions between particles are necessary for a reaction to occur, an increase in temperature leads to an increase in the frequency of collisions. Therefore, the rate of reaction increases as the temperature increases.
6.
A catalyst is best defined as a substance which increases the speed of a chemical reaction and which ___________ ______________ ______________.
Correct Answer
remains chemically unchanged
Explanation
A catalyst is a substance that speeds up a chemical reaction without being consumed or undergoing any permanent chemical changes itself. It provides an alternative pathway for the reaction to occur, lowering the activation energy required for the reaction to proceed. This allows the reaction to occur more quickly, but the catalyst itself remains unchanged and can be used repeatedly in future reactions.
7.
Which of the following industrial processes does not use a catalyst?
Correct Answer
C. Electrolysis of sodium chloride
Explanation
Electrolysis of sodium chloride is the process of breaking down sodium chloride into its constituent elements, sodium and chlorine, using an electric current. This process does not involve the use of a catalyst. In contrast, the oxidation of sulfur dioxide and the synthesis of ammonia both typically require the use of catalysts to facilitate the reaction.
8.
When an excess of calcium carbonate reacts with dilute hydrochloric acid, the reaction becomes slower and finally stops because
Correct Answer
D. The hydrochloric acid is all used up
Explanation
In this reaction, calcium carbonate reacts with hydrochloric acid to produce calcium chloride, carbon dioxide gas, and water. As the reaction proceeds, carbon dioxide gas is released in the form of bubbles. These bubbles can cover the surface of the calcium carbonate, forming a layer that hinders further reaction. However, the reaction ultimately stops because all of the hydrochloric acid is consumed in the reaction. Once the hydrochloric acid is completely used up, there are no more reactants available for the reaction to continue.
9.
In each of four different experiments, the same mass of magnesium reacts with the same volume of excess sulfuric acid.
Which set of conditions will result in the magnesium being used up the fastest?
Correct Answer
D. Powdered magnesium, 1 mol/dm3 of acid, 80 degrees celsius
Explanation
The powdered magnesium will react faster because it has a larger surface area compared to ribbon magnesium. This increased surface area allows for more frequent collisions between the magnesium particles and the acid molecules, leading to a higher reaction rate. Additionally, the higher concentration of acid (1 mol/dm3) and the higher temperature (80 degrees celsius) both contribute to an increase in reaction rate according to the collision theory.
10.
1. C(s) + CO2(g) ---> 2CO(g)
2. 2SO2(g) + O2(g) ---> 2SO3(g)
3. N2(g) + 3H2(g) ---> 2NH3 (g)
4. NaOH(aq) + HCl(aq) ---> NaCl(aq) + H2O(l)
The rate of reaction 4 is least likely to get affected by pressure.
Correct Answer
A. True
Explanation
The rate of reaction 4, NaOH(aq) + HCl(aq) ---> NaCl(aq) + H2O(l), is least likely to be affected by pressure because it does not involve any gaseous reactants or products. Pressure primarily affects reactions involving gaseous substances, as it can influence the concentration and collisions of gas particles. In reaction 4, all the reactants and products are in the aqueous phase, so changes in pressure will have minimal impact on the rate of the reaction.