Chemical Energetics EASE 2 Past papers Grade 10

During the burning reaction of methane the amount of energy given out is 780 kJ / mol.

Which one is true about the chemical energy changes?

• A

• B

• C

• D

Answer explanation

2 kata yg menunjukkan reaksi eksothermic : energy given out dan burning reaction

Reaksi pembakaran adalah eksothermik

ΔH negatif

Energy mengalir dari sistem ke lingkungan (release energy)

Temperature surrounding naik (lebih panas)

Reaksi exothermic yg sering keluar di EASE

-burning/combustion

-neutralisation (asam dan basa/alkali)

-metal + acid

-dilution of acid (pengenceran asam dengan ditambah air)

untuk perubahan fisika eksothermic

-freezing (membeku)

-condensation (misal mengembun)

Which of the following statements best describes the activation energy of a reaction?

• The minimum energy released when colliding particles react.

• The minimum energy required for particles to react when they collide.

• The maximum energy required for particles to react when they collide.

• The maximum energy released when colliding particles react.

Answer explanation

Energi aktivasi adalah jumlah energi minimum yang diperlukan untuk memulai suatu reaksi kimia. Energi ini diperlukan untuk memecahkan ikatan kimia dalam pereaksi sehingga mereka dapat berinteraksi dan membentuk produk baru.

Dalam diagram energi, energi aktivasi biasanya digambarkan sebagai puncak yang harus dilalui oleh pereaksi sebelum berubah menjadi produk.

Methane combusts in oxygen as shown producing an energy change of -890 kJ / mol

What is the bond energy of the C＝O ?

• -841 kJ/mol

• +841 kJ/mol

• -1682 kJ/mol

• +1682 kJ/mol

Answer explanation

ΔH = total bond energies broken - total bond energies formed

= Σ bond energi reaktan - Σ bond energi produk

ΔH = (4 x C-H + 2 x O=O) - (2 x C=O + 4 x O-H)

-890 = (4 x 410 + 2 x 496) - (2 x C=O + 4 x 460)

C=O = 841 kJ/mol

ΔH bisa positif/negatif tapi BOND ENERGY pasti positif

The reaction pro le for making nitrogen monoxide, NO, is shown below:

What is the activation energy for this reaction?

• -330

• +140

• +180

• +320

Answer explanation

Activation energy = energy dari reaktan sampai puncak

ΔH = selisih energy reaktan dan produk

Nitrogen reacts with hydrogen to produce ammonia.

What is the energy change for this reaction?

• 87 kJ / mol

• -87 kJ / mol

• 1473 kJ /mol

• -1473 kJ /mol

Answer explanation

ΔH = total bond energies broken - total bond energies formed

= Σ bond energi reaktan - Σ bond energi produk

ΔH = (1 x N≡N + 3 x H-H) - (6 x N-H)

= (945 + 3 x 436) - (6 x 390)

= -87

Which diagram is a correctly labelled reaction pathway diagram for an exothermic reaction?

• 
• 
• 
• 

Answer explanation

Energi aktivasi dimulai dari energi reaktan sampai energy puncak di diagram

ΔH (energy change) selisih energi reaktan dan produk di diagram

Exothermic mengeluarkan energy, energy produk lebih rendah dari reaktan di diagram

Which of the following changes are exothermic?

1.Burning of hydrogen to form water

2.Boiling water to form steam

3.Adding concentrated hydrochloric acid into water

• 1, 2 and 3

• 1 and 2

• 1 and 3

• 1 only

Answer explanation

Burning (pembakaran) selalu eksothermik

Perubahan fisika padat ke cair dan cair ke gas menyerap energy (endothermik)

Adding acid to water (pengenceran asam) selalu eksothermik

Reaksi exothermic yg sering keluar di EASE

-burning/combustion

-neutralisation (asam dan basa/alkali)

-metal + acid

-dilution of acid (pengenceran asam dengan ditambah air)

untuk perubahan fisika eksothermic

-freezing (membeku)

-condensation (misal mengembun)

untuk perubahan fisika endothermic

-melting (meleleh)

-boiling/evaporating (mendidih/menguap)

Which row identifies a chemical and a physical change?

• A

• B

• C

• D

Answer explanation

Pelarutan (dissolving) selalu perubahan fisika, Kecuali jika zat terlarut bereaksi dengan air

misal CaO + H₂O → Ca(OH)₂

2Na + H₂O → 2NaOH + 2H₂

Burning dan combustion (reaksi pembakaran) perubahan kimia

Kata2 perubahan wujud yg menunjukkan perubahan fisika : melting, evaporating, freezing, condensation, sublimation

The temperature of the water in two beakers, X and Y, is measured as 21.5 °C.

5 g of sodium chloride is dissolved in the water in beaker X. The temperature changes to 18.0 °C.

5 g of calcium oxide is dissolved in the water in beaker Y. The temperature changes to 29.4 °C.

Which types of process are occurring in beakers X and Y?

• Both beaker X and Y are endothermic process

• In beaker X is endothermic process, while in beaker Y is exothermic process

• In beaker X is exothermic process, while in beaker Y is endothermic process

• Both beaker X and Y are exothermic process

Answer explanation

Kenaikan suhu menunjukkan reaksi exothermic. Suhu surrounding lebih panas setelah proses reaksi

Penurunan suhu menunjukkan reaksi exothermic. Suhu surrounding lebih panas setelah proses reaksi

*miskonsepsi : ketika air didinginkan suhu air turun menjadi dingin apakah ini endothermic?

• Ketika kits memasukkan air ke dalam kulkas, kulkas menyerap panas dari air dan membuangnya ke udara di luar kulkas. Hasilnya, air kehilangan energi panas dan suhunya menurun. (air disini sebagai sistem bukan lingkungan)

Nilous observing a reaction using a calorimeter and measured 150 kJ of heat has been released from the reaction and the total energy to start the reaction is 128 kJ.

Which of the following graphs best represents the reaction above?

• 
• 
• 
• 

Answer explanation

Energi aktivasi dimulai dar energi reaktan sampai energy puncak di diagram

ΔH (energy change) selisih energi reaktan dan produk di diagram

Exothermic mengeluarkan energy, energy produk lebih rendah dari reaktan di diagram

150 kJ heat released artinya eksothetmic panah kebawah

total energy to start the reaction is 128 kJ artinya E_anya 128 kJ