Rates of reaction Flashcards
Rate of reaction definition?
The change in concentration of a reactant or product in unit time
What is rate of reaction measured in?
mol dm^-3 s^-1
What does higher pressure do to the rate of reaction?
Increases it, as more frequent collisions
How can a chemical reaction be monitored?
Colour change
Change in mass
Volume of gas produced
Conductivity
Rate of reaction formula?
Change in concentration/ change in time
How can you measure the rate of reaction at a certain point on a concentration- time graph?
Find the gradient of the tangent
Catalyst definition?
A substance that increases the rate of a chemical reaction, without being used up in the process. By providing an alternative route for the reaction with lower activation energy
What’s a heterogeneous catalyst?
One in a different physical state from the reactants, most frequently gaseous reactants, and solid catalyst
What’s a homogenous catalyst?
One in the same physical state as the reactants, normally aqueos of gaseous state
What are the sustainable and economic importance of catalysts?
Reduce energy consumption, and therefore reduced effect on environment
Also less energy used in heating reaction, so increased profits
How to draw a Boltzman distribution?
Curve starts at (0,0)
Goes up in straight line then slopes down, then slopes off
X axis= kinetic energy
Y axis= Number of particles
Label the activation with a vertical line at tail
What does the area under a Boltzman distribution represent?
Total number of particles in the system
Which proportion of molecules have more than the kinetic energy and therefore can react?
The area after the EA line
What happens to the Boltzman distribution if you increase the temperature?
Peak gets lower, and moves to a higher energy
Tail will there be higher when passing the EA
What happens to the proportion of molecules with at least the activation energy when the temperature increases?
Increases
What happens to Boltzman distribution when you add a catalyst?
EA decreases
Why does increasing the concentration of reactant or pressure of reactant increase rate of reaction?
More particles per unit volume, so more frequent collisions
How does grinding the solid reactant into a powder increase the rate of reaction?
Increased surface area of contact, so more frequent collisions
What is meant by activation energy, and why do most chemical reactions require one?
Minimum energy required to start a reaction (by the breaking of bonds), and most reactions require bonds to be broken in reactant molecules
Definition of rate equation for the reaction A + B = C ?
Rate = K ((A)^m)((B)^n)
where m and n are the order of reaction (0, 1 or 2)
Rate= rate in mol dm^-3 s^-1
K= rate constant
A and B are the concentrations of the chemicals in mol dm^-3
Definition of order of reaction?
The power to which the concentration of reactant is raised in the rate equation
Definition of rate constant?
The constant that links the rate of reaction with the concentrations of the reactants raised to the power of their orders in the rate equation
Zero order reaction on a Rate-conc graph?
Horizontal line
1st order reaction on a Rate-conc graph?
starts at origin and is diagonal line
