Question Analysis: The graph typically provided in this context plots the concentration of the reactant $[R]$ versus time $t$ for a straight line with a negative slope.

Step 1 (Governing Law & Identification): [0.5 Mark]

For a zero-order reaction, the integrated rate equation is given by:

Comparing this with the equation of a straight line, $y = mx + c$, where $y = [R]$ and $x = t$, we identify the reaction kinetics.

Step 2 (Mathematical Working): [1.0 Mark]

• Part (a): Since the plot of $[R]$ versus $t$ is a straight line, the rate of reaction is independent of the concentration of the reactant. Therefore, the order of the reaction is zero.
• Part (b): From the integrated rate equation $[R] = -kt + [R]_0$, the slope ($m$) of the curve is the coefficient of the variable $t$.
$$m = -k$$

Step 3 (Final Concluded Answer): [0.5 Mark]

• (a) Order of reaction: Zero order ($n = 0$).
• (b) Slope of the curve: $-k$ (where $k$ is the rate constant).

💡 EL10 Concept Insight: Imagine a candle burning at a constant speed regardless of how long it has been burning; because the amount of candle left decreases steadily over time in a straight line, we call this a "zero-order" reaction.