Question

(a) If you were going to build a system to check the effectiveness of automobile catalytic converters on cars, what substances would you want to look for in the car exhaust? (b) Automobile catalytic converters have to work at high temperatures, as hot exhaust gases stream through them. In what ways could this be an advantage? In what ways a disadvantage? (c) Why is the rate of flow of exhaust gases over a catalytic converter important?

Short answer

(a) To check the effectiveness of automobile catalytic converters, look for Carbon Monoxide (CO), Unburned Hydrocarbons (HC), and Nitrogen Oxides (NOx) in the car exhaust. (b) Advantages of high temperatures in catalytic converters include faster conversion of harmful substances and improved fuel efficiency. Disadvantages include thermal stress to the catalytic converter and overheating of surrounding components. (c) The rate of flow of exhaust gases over a catalytic converter is important to ensure efficient conversion of harmful substances, prevent overheating, and maintain proper exhaust backpressure for optimal engine performance and fuel efficiency.

Step-by-step solution

(a) Substances in car exhaust

To evaluate the effectiveness of automobile catalytic converters, one should look for the following substances in the car exhaust: 1. Carbon Monoxide (CO): A harmful and poisonous gas that needs to be converted into carbon dioxide (CO2). 2. Unburned Hydrocarbons (HC): Unburned fuel particles that need to be converted into CO2 and water (H2O). 3. Nitrogen Oxides (NOx): Pollutants that need to be reduced to nitrogen (N2) and oxygen (O2). An effective catalytic converter will convert these harmful substances into less harmful ones.

(b) High temperatures in catalytic converters: advantages and disadvantages

Advantages: 1. Faster conversion of harmful substances: High temperatures increase the efficiency of the chemical reactions occurring in the converter, helping to quickly convert harmful substances into less harmful ones. 2. Improved fuel efficiency: An automobile engine performs more efficiently at higher temperatures, which can lead to improved fuel efficiency and reduced fuel consumption. Disadvantages: 1. Thermal stress to the catalytic converter: High temperatures cause expansion and contraction, which can cause thermal stress and possible damage to the catalytic converter over time. 2. Overheating of surrounding components: The high operating temperature of the catalytic converter may indirectly affect surrounding components (such as heat shields, exhaust pipes, and bodywork) by exposing them to extreme heat.

(c) Importance of the rate of flow of exhaust gases

The rate of flow of exhaust gases over a catalytic converter is important for several reasons: 1. Ensures efficient conversion of harmful substances: A proper flow rate ensures that the harmful substances in the exhaust gases have sufficient time to react with the catalyst, resulting in their efficient conversion to less harmful compounds. 2. Prevents overheating: If the flow rate is too high, it can lead to overheating of the catalytic converter, potentially causing damage and reducing its efficiency. 3. Maintains proper exhaust backpressure: The right flow rate helps maintain proper backpressure in the exhaust system, which is necessary for optimal engine performance and fuel efficiency. Too high or too low flow rate can negatively impact engine performance and fuel consumption.