Practice Endothermic Reaction in Chemistry

Use these practice problems to test your method after reviewing the concept explanation and worked examples.

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Quick Recap

A chemical reaction that absorbs energy (usually as heat) from the surroundings, resulting in a decrease in surrounding temperature and a positive enthalpy change (ฮ”H>0\Delta H > 0).

The reaction needs heat to proceed โ€” you can feel the surroundings get colder as it runs.

Showing a random 20 of 50 problems.

Example 1

hard
N2(g)+O2(g)โ†’2NO(g)\text{N}_2(g) + \text{O}_2(g) \rightarrow 2\text{NO}(g) has ฮ”H=+180โ€‰kJ\Delta H = +180\,\text{kJ}. How much heat is absorbed when 14โ€‰g14\,\text{g} of N2\text{N}_2 reacts? (N2=28โ€‰g/mol\text{N}_2 = 28\,\text{g/mol})

Example 2

challenge
A student says an endothermic reaction with a catalyst becomes exothermic because it now starts easily. Critique this.

Example 3

medium
Photosynthesis stores 2870 kJ per mole of glucose formed. State ฮ”H\Delta H and classify.

Example 4

medium
An endothermic reaction has ฮ”H=+120โ€‰kJ\Delta H = +120\,\text{kJ} and Ea=200โ€‰kJE_a = 200\,\text{kJ}. What is EaE_a for the reverse reaction?

Example 5

medium
A reaction has ฮ”H=+180\Delta H = +180 kJ. Is it endothermic, and how much energy is absorbed?

Example 6

easy
Cooking an egg requires continuous heat input. Is this an endothermic or exothermic process?

Example 7

easy
For an endothermic reaction, energy can be treated as a reactant. True or false?

Example 8

medium
Photosynthesis absorbs 2803 kJ per mole of glucose. Is it endothermic or exothermic? What is the sign of ฮ”H\Delta H?

Example 9

medium
Why does an endothermic reaction mixture often feel cold to the touch?

Example 10

medium
Can an endothermic reaction occur spontaneously? Explain briefly.

Example 11

easy
When an endothermic reaction runs, does the surroundings or the system get cold?

Example 12

easy
On an energy diagram, are the products higher or lower than reactants for an endothermic reaction?

Example 13

medium
A reaction absorbs 75 kJ. Write its ฮ”H\Delta H with sign and classify it.

Example 14

medium
Why does dissolving table salt feel only slightly cool (vs ammonium nitrate, which feels strongly cool)?

Example 15

medium
Breaking the H-H bond in H2\text{H}_2 requires 436โ€‰kJ/mol436\,\text{kJ/mol}. Is bond-breaking endothermic?

Example 16

hard
On an energy diagram, an endothermic reaction has activation energy 150โ€‰kJ150\,\text{kJ} and ฮ”H=+40โ€‰kJ\Delta H = +40\,\text{kJ}. How far below the transition state are the products?

Example 17

easy
What is the sign of ฮ”H\Delta H for an endothermic reaction?

Example 18

challenge
An endothermic reaction has Ea=120E_a = 120 kJ and ฮ”H=+60\Delta H = +60 kJ. How far below the peak are the products, measured from the peak?

Example 19

medium
An instant cold pack contains ammonium nitrate and water. When the inner bag is broken, the temperature drops from 25ยฐC25ยฐ\text{C} to 5ยฐC5ยฐ\text{C}. Classify the process and explain.

Example 20

easy
A reaction has ฮ”H=+45โ€‰kJ\Delta H = +45\,\text{kJ}. Classify it.
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