Credit: Courtesy of Ramos Keith, US Fish and Wildlife Service
License: CC BY-NC 3.0
How harmful are forest fires?
Forest fires cause extensive damage when they occur. Both plant and animal life are harmed during these events. The severity of a forest fire depends on how much plant life is available to burn – the more available dry plant material, the more serious the fire and the more rapidly it will spread.
Order of Reaction
In the reaction A→B, the rate of the reaction is directly proportional to the concentration of A raised to the first power. That is to say, [A]=[A]1. A first-order reaction is a reaction in which the rate is proportional to the concentration of only one reactant. As a first-order reaction proceeds, the rate of reaction decreases because the concentration of the reactant decreases (see Figure below). The graph of concentration versus time is curved. The reaction rate (Δ[A]Δt) can be determined graphically by the slope of a tangent to the curve at any point. The rate of the reaction at the time shown with the red triangle is given by:
rate=−[A]final−[A]initialΔt=−0.35 M−0.63 M3.0 s−1.0 s=0.14 M/s
Credit: CK-12 Foundation - Christopher Auyeung
License: CC BY-NC 3.0
This graph shows how the concentration of a reactant changes as a reaction proceeds. The rate of the reaction is determined at any point by measuring the slope of a tangent to the curve.[Figure2]
The rates of some reactions depend on the concentrations of more than one reactant. Consider a reaction in which a molecule of A collides with a molecule of B to form product C.
Doubling the concentration of A alone would double the reaction rate. Likewise, doubling the concentration of B alone would also double the rate. The rate law must reflect the rate dependence on both reactants.
This reaction is said to be first order with respect to A and first order with respect to B. Overall, it is a second-order reaction. The rate law and the order of a reaction must be determined experimentally.
- A first-order reaction is described.
- What is a first-order reaction?
- How is the instantaneous rate determined?
- How do we determine rate law and reaction order?