Question

2.1 g of a hydrocarbon fuel is burned in a calorimeter that contains 280 grams of water initially at 25.00◦C. After the combustion, the temperature is 26.55◦C. How much heat is evolved per gram of fuel burned? The heat capacity of the calorimeter (hardware only) is 92.3 J/◦C.

Answer 1

Answer:

$\large \boxed{\text{933 J}}$

Explanation:

There are three heat transfers involved.

heat from combustion of propane + heat gained by water + heat gained by calorimeter = 0

  q₁     +     q₂      +       q₃      = 0

m₁ΔH + m₂C₂ΔT + C_calΔT = 0

Data:

 m₁ =      2.1   g

 m₂ = 280     g

   Ti = 25.00 °C

   T_f = 26.55 °C

Ccal = 92.3 J·°C⁻¹

Calculations:

Let's calculate the heats separately.

1. q₁

q₁ = 2.1 g × ΔH = 2.1ΔH g

2. q₂

ΔT = T_f - Ti = 26.55 °C - 25.00 °C = 1.55 °C

q₂ = 280 g × 4.184 J·°C⁻¹ × 1.55 °C = 1816 J

3. q₃

q₃ = 92.3 J·°C⁻¹ × 1.55 °C = 143.1 J

4. ΔH

$\begin{array}{rcl}\text{2.1 \Delta H g +1816 J +143.1 J} & = & 0\\\text{2.1 \Delta H g +1959 J} & = & 0\\\text{2.1 \Delta H g}& = & \text{-1959 J}\\\Delta H & = & \dfrac{\text{-1959 J}}{\text{2.1 g}}\\\\& = & \textbf{-933 J/g}\\\end{array}\\\text{The combustion releases \large \boxed{\textbf{933 J}} per gram of fuel burned.}$