Chapter 5.3 Catalyst Flashcards
Explain why the catalyst is more effective when coated onto an unreactive honeycomb.
- Increase in surface area,
- rate of successive collisions increase
Explain why a small increase in temperature has a large effect on the initial rate of a reaction.
There is a small increase in temperature results in collisions with energy greater than the activation energy
What is the effect of an increase in temperature on the rate of a chemical reaction?
Explain your answer with reference to the Maxwell–Boltzmann distribution.
Effect
Explanation. (2)
Effect - rate of reaction increases
Explanation - more particles have activation energy
What is the effect of the addition of a catalyst on the rate of a chemical reaction?
Explain your answer with reference to the Maxwell–Boltzmann distribution.
Effect
Explanation
Effect - rate of reaction increases,
Explanation - lowers the activation energy so that more molecules are able to react
Give one reason why the reaction between hydrogen and chlorine is very slow at room temperature. (1)
-activation energy is high, very few particles have the energy to react
Explain why an increase in pressure, at constant temperature, increases the rate of reaction between hydrogen and chlorine
- more particles In a given volume
- therefore more collision
Explain why a small increase in temperature can lead to a large increase in the rate of reaction between hydrogen and chlorine
Many more molecules have energy greater than the activation energy
Give the meaning of the term catalyst
Speeds up a reaction but is chemically unchanged
Suggest one reason why a solid catalyst for a gas-phase reaction is often in the form of a powder
increases the surface area
The rate of a chemical reaction may be increased by an increase in reactant concentration, by an increase in temperature and by the addition of a catalyst.
State which, if any, of these changes involves a different activation energy. Explain your answer
Change
Explanation (4)
Change = catalyst Explanation = with a catalyst being present the activation energy is lowered so more molecules can react
State one way in which the collision frequency between particles in a gas can be increased without changing the temperature.
Increase concentration or pressure
Explain In general terms how a catalyst works (3)
- lowers the activation energy,
- so more molecules are able to react,
- alternative route
equation for the decomposition of hydrogen peroxide is shown below.
2H2O2 = 2H2O + O2
State the measurements you would take in order to investigate the rate of this reaction
-measure volume of gas at regular time intervals
State what is meant by the term rate of reaction
Change in concentration of a substance per unit time
Give two reasons, other than an increase in the reaction rate, why these equations suggest that hydrogen bromide is behaving as a catalyst
- remains unchanged ,
- alternative route
Magnesium ribbon reacts with hot water. Heated magnesium ribbon reacts with steam. State two differences between these reactions.
- hot water produces the hydroxide,
- steam produced the oxide
In terms of collision theory explain why, at a fixed temperature, the rate of this reaction doubles when the concentration of the hydrochloric acid doubles.
- twice the amount of HCL in a given volume,
- twice the amount of successive collisions per unit time
Give one reason, other than the increase in rate of reaction, why the student was able to deduce that hydrogen bromide behaves as a catalyst in this two-step reaction
-hydrogen bromide was unchanged at the end of the reaction
