At 518oC, the rate of decomposition of a sample of gaseous acetaldehyde, initially at a pressure of 363Torr, was 1.00Torrs−1 when 5% had reacted and 0.5Torr s−1 when 33% had reacted. The order of the reaction is:

The order of a reaction can be determined by examining how the rate of reaction changes with the concentration of the reactants.

In this case, we are given two sets of data:

1. When 5% of the acetaldehyde had reacted, the rate of reaction was 1.00 Torr/s.
2. When 33% of the acetaldehyde had reacted, the rate of reaction was 0.5 Torr/s.

We can use these data to calculate the order of the reaction.

First, we need to calculate the initial concentration of the acetaldehyde. The initial pressure was 363 Torr, so the initial concentration is proportional to this value.

Next, we calculate the concentrations at the two given points in the reaction. When 5% had reacted, the concentration was 95% of the initial concentration. When 33% had reacted, the concentration was 67% of the initial concentration.

We can then set up the following equation, where k is the rate constant and n is the order of the reaction:

(1.00 Torr/s) / (0.95 * 363 Torr)^n = (0.5 Torr/s) / (0.67 * 363 Torr)^n

Solving this equation for n will give us the order of the reaction.

Please note that this is a simplified explanation and the actual calculation may require more complex mathematical manipulation.