H2C=CH2(g) + H2(g) C2H6(g)

Adding a small amount of platinum powder greatly increases the rate of the reaction above. How might the platinum be affecting the rate of the reaction? (Select all that apply.)

1) It increases the concentration of the reactants.
2) It increases the temperature of the reaction.
3) It lowers the energy of activation for the reaction.
4) It orients the reactants in the proper direction.
5) It increases the energy of activation for the reaction.
6) It acts as a catalyst in the reaction.

3 and 6 (but 3 is how 6 works).

To determine how platinum powder affects the rate of the given reaction, we need to understand the role of catalysts.

A catalyst is a substance that increases the rate of a chemical reaction by providing an alternative reaction pathway with lower activation energy. It remains unchanged at the end of the reaction. Catalysts do not directly participate in the reaction, but they accelerate the rate of the reaction by providing an alternative mechanism.

Now, let's analyze the options provided:

1) It increases the concentration of the reactants.
Platinum does not affect the concentration of the reactants in the system. Therefore, this option is not correct.

2) It increases the temperature of the reaction.
Platinum, being a solid catalyst, does not directly affect the temperature of the reaction. It does not release heat or change the temperature. Therefore, this option is not correct.

3) It lowers the energy of activation for the reaction.
This statement is true. Catalysts, like platinum powder, provide an alternative reaction pathway with a lower activation energy. By lowering the energy barrier, more reactant molecules can overcome it and form products more quickly. Therefore, platinum powder does lower the energy of activation for the given reaction.

4) It orients the reactants in the proper direction.
Platinum does not directly orient the reactants. Orientation of reactants is usually seen in reactions that involve a specific arrangement of molecules due to their shape or structure. Therefore, this option is not correct.

5) It increases the energy of activation for the reaction.
This option is not correct. Catalysts do not increase the energy of activation in a reaction; rather, they lower it.

6) It acts as a catalyst in the reaction.
This statement is true. Platinum powder acts as a catalyst in the given reaction by providing an alternative pathway with lower activation energy, thereby increasing the reaction rate.

Based on the explanations provided, the correct answers for how platinum powder affects the rate of the reaction are:
- It lowers the energy of activation for the reaction.
- It acts as a catalyst in the reaction.