Rate Expressions

[SAMPLE question] Chemical reactions may be classified based on their reaction rate expressions

• True

• False

Answer explanation

True

Today we're going to know that there are different types of chemical reactions according to their reaction rate expressions

Tags

NGSS.HS-PS1-5

[BLIND question] Which are the components of a reaction rate expression?

• rate constant (k) + function of concentrations f(C_A)

• function of concentrations f(C_A) + reaction temperature (T)

• rate constant (k) + reaction temperature (T)

• reaction time (t) + reaction temperature (T)

Answer explanation

A reaction rate is usually expressed as follows:

-r_A = k * f(C_A)

Tags

NGSS.HS-PS1-5

[REINFORCEMENT question] According to the previous definition of a reaction rate expression -r_A = k f(C_A) which of the following could be an example?

• -r_A = C_A²/T

• -r_A = kT

• -r_A = k C_A

• -r_A = T/t

Answer explanation

In this case:

k = k

f(C_A) = C_A

Therefore:

-r_A = k f(C_A) = k C_A

Tags

NGSS.HS-PS1-5

[BLIND question] Several chemical reactions follow a power-law model like

f(C_A) = C_A^α

where α is a number (0, 1, 2...)

Which of the following expressions doesn't follow that model?

• -r_A = kC_A

• -r_A = k

• -r_A = kC_A²

• -r_A = kT³

Answer explanation

-r_A = k is valid when α = 0

-r_A = kT³ doesn't represent a reaction rate expression

Tags

NGSS.HS-PS1-5

[REINFORCEMENT question] According to the power law, a second order reaction (α = 2) could be expressed as:

• -r_A = kC_A²

• -r_A = kC_A

• -r_A = kC_A^1/2

• -r_A = k

Answer explanation

-r_A = kC_A^α

If: α = 2

-r_A = k C_A²

Tags

NGSS.HS-PS1-5