Which of the following processes is endothermic?
Correct answer B. Thermal decomposition of calcium carbonate
Subject / 763 questions
MDCAT ECAT Chemistry MCQs
Page 30 of MDCAT ECAT Chemistry multiple-choice questions with answers. Tap an option to check yourself.
Page 30 of 39
- Gases 40
- Liquids 40
- Solids 40
- Chemical Equilibrium 40
- Reaction Kinetics 40
- Thermochemistry and Energetics 40
- Electrochemistry 40
- Fundamental Concepts of Chemistry 40
- Atomic Structure 39
- Chemical Bonding 39
- Alcohols and Phenols 38
- Industrial Chemistry 37
- Aldehydes and Ketones 37
- Alkyl Halides 37
- s- and p-Block Elements 37
- Chemistry of Hydrocarbons 36
- Fundamental Principles of Organic Chemistry 36
- Carboxylic Acids 36
- Transition Elements 35
- Macromolecules 35
Which of the following is a state function?
Correct answer B. Enthalpy
An ideal sealed vacuum flask allows neither heat nor matter to cross its walls. What kind of system does its contents represent?
Correct answer C. Isolated system
Advertisement
Which equation expresses the first law of thermodynamics, using the convention that work done on the system is positive?
Correct answer D. ΔU = q + w
A system absorbs 250 J of heat and does 100 J of work on the surroundings. What is the change in its internal energy?
Correct answer B. +150 J
Under what condition is the heat exchanged in a reaction equal to its enthalpy change, ΔH?
Correct answer B. At constant pressure
In a bomb calorimeter the reaction takes place in a sealed steel vessel. Which quantity does the heat measured correspond to directly?
Correct answer A. ΔU, the change in internal energy
Which statement is Hess’s law?
Correct answer A. The total enthalpy change of a reaction is the same whatever route is taken, provided the initial and final states are the same
Given C(s) + O₂(g) → CO₂(g), ΔH = −393.5 kJ mol⁻¹ and CO(g) + ½O₂(g) → CO₂(g), ΔH = −283.0 kJ mol⁻¹, what is ΔH for C(s) + ½O₂(g) → CO(g)?
Correct answer B. −110.5 kJ mol⁻¹
Advertisement
According to the Arrhenius equation, k = A e^(−Ea/RT), how does the rate constant change if a reaction has a larger activation energy at the same temperature?
Correct answer A. k becomes smaller
The rate of a reaction doubles for every 10 °C rise in temperature. By what factor does the rate increase when the temperature rises from 20 °C to 50 °C?
Correct answer C. 8
When the concentration of reactant A is tripled while other conditions stay the same, the rate increases nine times. What is the order with respect to A?
Correct answer B. 2
The acid-catalysed hydrolysis of ethyl ethanoate in a large excess of water behaves kinetically as which type of reaction?
Correct answer C. Pseudo-first order
For a zero-order reaction, how does the rate change when the reactant concentration is doubled?
Correct answer B. The rate does not change
A reaction has the rate equation rate = k². What are the units of k when concentrations are in mol dm⁻³ and time is in seconds?
Correct answer A. dm⁶ mol⁻² s⁻¹
Advertisement
Which statement correctly distinguishes molecularity from order of reaction?
Correct answer D. Molecularity applies to an elementary step and is always a whole number, while order can be zero or fractional
Which of the following best defines the rate of a chemical reaction?
Correct answer C. The change in concentration of a reactant or product per unit time
What are the usual SI-based units for the rate of a reaction in solution?
Correct answer D. mol dm⁻³ s⁻¹
For 2N₂O₅(g) → 4NO₂(g) + O₂(g), N₂O₅ is used up at 0.020 mol dm⁻³ s⁻¹. What is the rate of formation of O₂?
Correct answer B. 0.010 mol dm⁻³ s⁻¹
How is the order of a reaction with respect to a reactant determined?
Correct answer B. Only by experiment