k in first order reactions

[Radha Patel 4I]

In section 7B, why are the rate constants for first order reactions positive ? If the plot of the first order reaction has a negative slope then shouldn't k be negative in the solutions?

[Ryan Yee 1J]

Rate constants are positive, but the slopes are negative because rate measures the disappearance of reactant (which is why k is negative). In a first order reaction, the negative of the slope is equal to k.

[Juliana Chopelas 1A]

Rate constants are always positive due to the Arrhenius equation but the slope is negative because it shows how the reactants are affected in the first order reaction.

[Helen Struble 2F]

Rate constants are always positive. In the plot of ln[A] by time, for first order reactions, the slope is equal to -k. So, while the slope is technically negative, the rate constant, as with any rate constant, is positive.