# Chemical Reaction Engineering Questions and Answers – Space Time and Space Velocity

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This set of Chemical Reaction Engineering Multiple Choice Questions & Answers (MCQs) focuses on “Space Time and Space Velocity”.

1. Space time is defined as ____
a) Time required to process unit volume of feed
b) Time required for the reaction to occur
c) Time required to produce unit volume of product
d) Time to process the entire volume of feed entering

Explanation: Space time is the time spent by a unit volume of reactants inside the reactor. It is the performance measure for a flow reactor.

2. The unit of space velocity is ____
a) sec
b) sec-1
c) m3
d) m-3

Explanation: Space velocity has the dimensions of time-1. A space velocity of 2 hr-1 implies that 2 reactor volumes are fed per hour.

3. Space time as a function of molar feed rate and initial concentration is given as ____
a) $$\frac{VC_{A0}}{F_{A0}}$$
b) $$\frac{C_{A0}}{VF_{A0}}$$
c) $$\frac{VF_{A0}}{C_{A0}}$$
d) $$\frac{C_{A0}}{F_{A0}}$$

Explanation: Space time is the ratio of the product of reactor volume and initial concentration to the feed rate. $$\frac{VC_{A0}}{F_{A0}}$$ has the same unit as that of space time.

4. If V represents volume and Q represents volumetric flow rate, then which of the following is a valid expression for space velocity?
a) $$\frac{V}{Q}$$
b) $$\frac{Q}{V}$$
c) Q × V
d) $$\frac{V}{C_{A0}}$$

Explanation: Space velocity is the ratio of volumetric flow rate to volume. It has the unit hr-1.

5. State true or false.
Space velocity is the number of unit volumes of feed that can be treated per unit time.
a) True
b) False

Explanation: Space velocity is the inverse of space time. It gives a measure of what volume of feed can be processed in a unit time.