OCR Chemistry A – 'How Fast' (5.1.1) Test1of2

TICK ALL THAT APPLY: the overall order of a reaction...

• is the sum of the all orders with respect to each reactant

• tells you the overall rate

• is k

• is 1^st-order when the units of k are (s^-1)

When the concentration of a second order reactant is increased by a factor of four...

• the rate constant quadruples

• the rate of reaction increases by a factor of eight

• an endothermic reaction will increase in temperature

• the slowest step increases in rate by a factor of 16

A student monitors the rate of a reaction and plots the concentration of one reactant against time.

What can be determined about this reaction?

• The reaction is zero order with respect to this reactant.

• The reaction is first order with respect to this reactant.

• The reaction is second order with respect to this reactant.

• The rate of reaction is constant.

Which order of reaction could each of these two concentration-time graphs represent?

• 1) 1^st-order 2) 2^nd-order

• 1) zero order 2) also zero order

• 1) zero order 2) 1^st-order

• 1) 1^st-order 1) also 1^st-order

Two conc.-time graphs are shown. Which of the following statements about graphs 1 and 2 could be true?

• graph 1 is zero order with respect to the conc. of a reactant

• with respect to the conc. of a product, graph 1 is zero order and graph 2 is 1^st-order

• the shape of the graph 2 does not reveal if it is 1^st- or 2^nd-order

• graph 2 is also the shape of a 2^nd-order rate vs. [reactant] graph.

TICK ALL THAT APPLY: this graph could represent

• the concentration of a product against time in a 2^nd-order reaction.

• the concentration of a product against rate in a 1^st-order reaction.

• how the rate varies with different initial concentration in a 2^nd-order reaction.

• how k varies with T (K)

TICK ALL THAT APPLY: the rate constant, k, can be calculated...

• by taking the y-axis value of a zero order rate-conc graph.

• from the rate equation, using initial concentrations and the rate

• from a 1st-order conc.-time graph, using the rate at any time point and the gradient at that same point.

• by calculating the gradient of a 1st-order rate-conc graph

• by: $\frac{\ln\left(2\right)}{t_{\frac{1}{2}}}$ , when the reaction is 2nd-order

TICK ALL THAT APPLY: the following are ways of continuously monitoring the rate of reaction

• absorbance via a colorimeter

• mass loss

• using a starch solution

• titration

• gas collection

BrO₃^–(aq) + 6I^–(aq) + 6H⁺ --> 3I₂(aq) + 3H₂O(l) + Br^–(aq)

What are the value and units of the rate constant?

• 0.48 dm³ mol^–1 s^–1

• 0.48 dm⁹ mol^–3 s^–1

• 4.8 dm^–6 mol² s^–1

• 4.8 dm⁶ mol^–2s^–1

CO(g) + NO₂(g) --> CO₂(g) + NO(g)

This reaction follows a two-step mechanism with a slow first step:

2NO₂(g) --> NO₃(g) + NO(g)

CO(g) + NO₃(g) --> CO₂(g) + NO₂(g)

What is the correct rate equation for the reaction?

• rate = k[CO][NO₃]

• rate = k[NO₂]²[CO][NO₃]

• rate = k[NO₂]²

• rate = k[NO₂]²[NO₃][NO]